- An unrevealed cylon draws 5 cards at the start of their turn. A revealed cylon only draws 2. Skill cards are worth 2.2 on average, so a revealed cylon draws 6.6 points of skill power less each time around the table.
- An unrevealed cylon can throw any number of cards into a skill check. A revealed cylon can only throw 1. This really means that a revealed cylon can't cause any given check to fail, but their existence does put extra pressure on the humans. Every skill check is potentially a little harder. An unrevealed cylon can pretty much guarantee any given skill check will fail, assuming they draw the right colour of cards.
- An unrevealed cylon is restricted to certain card types. A revealed cylon can draw any colour card, including treachery. Unfortunately the treachery deck sucks, and is only worth 1.8 on average with a max of 3. The colour split only really matters if the unrevealed cylon has a very restricted colour set. Yellow and green tend to be positive, so it's harder to make a check fail if that's all you draw. Someone who draws lots of red and blue cards is in a great position to make skill checks fail.
- An unrevealed cylon has access to their character abilities, which can include some truly powerful once per game abilities. If Cally reveals without executing a human first it's probably a huge mistake, for example.
- A revealed cylon gets access to the cylon board spaces. Generally speaking the cylon board spaces will inflict more damage than the human board spaces. Way more damage. Most human spaces can only help the humans along. Probably the best you can do is draw extra cards or play 'launch scout' cards.
- An unrevealed cylon can hold a title. The admiral gets to choose the next destination and controls the nukes, both of which are very powerful abilities. The president can potentially draw cards to throw people in the brig. The CAG can't really hurt the humans, and they have to be pretty blatant to refuse to help the humans, but it's still something.
- An unrevealed cylon who plays it straight seeds potential confusion and disruption amongst the humans. As soon as the cylons have revealed the rest of the humans gain complete trust with each other. This has to have some benefit, but it's really hard to quantify and depends on the paranoia level of the other players. It seems like staying unrevealed has the potential to put Andrew on tilt, for example!
- An unrevealed cylon can be targeted by actions which hurt humans. They can be thrown in the brig, they can be sent to sick bay, and they can be executed. They can be forced to discard cards. If you've played it really straight you probably won't be abnormally hit by these, but if you've been at all shady you might well get hit. I've often said it's just fine to force the humans to waste a bunch of cards throwing you in the brig, but there are crisis cards with 'failure' conditions which force the humans to do bad things to one of their own. Having an unrevealed cylon as a target for these penalties is awesome for the humans. They don't need to pass the skill check, they get to hurt the cylons, and they don't get hurt themselves.
- A cylon that reveals on their own accord (not executed or in the brig) gets to use a powerful special ability when they reveal, they get to draw a powerful super crisis card, and they get to keep 3 cards from their hand. A cylon that reveals from the brig still gets the super crisis card. A cylon that is executed has to discard their hand and gets nothing special.
- Cylons don't get a crisis card at the end of their turn. This both slows down the damage done to the humans and slows down their progress towards game end. The lack of jump prep (which is apparently on 67% of the base game cards) is the biggest reason I've always wanted to reveal early. But is the extra damage done from those crisis worth it? On the one hand they're going to need the same number of jump prep to end the game so they're going to hit the same amount of damaging crisis cards along the way. As such revealing has to be good, because you can throw non-crisis damage their way. On the other hand by spreading those crisis cards out over more rounds around the table the humans get to draw more cards to use passing them.
Unrevealed cylons actually have the advantage in almost all of these bullet points. Some of the advantages are pretty big, even. Holding the admiral title, using your once per game ability, and being able to make a skill check fail are all huge. On the other hand the advantages you gain for actually revealing are really powerful. The revealing ability tends to do at least as much damage as failing a crisis, and the super crisis cards are often worth the damage of a couple crisis cards as well. Slowing the game down by denying jump prep is actually good. I think staying unrevealed to sow discord sounds really good, but doesn't really work out. If you do minor damage while staying unrevealed you risk a crisis coming up which brigs/executes a human player and then you're in big trouble. Getting executed for free is brutal. Even getting thrown out the airlock is pretty bad.
I feel like in a game with inexperienced players, where you can do minor damage and get away with it, or where you can really making someone else seem suspicious then it can be worth sticking around. If you can manage to stick around and cause multiple crisis skill checks to fail it'll be awesome for you. But I'd always be keeping my eye out for a way to do some blatant damage and reveal as soon as possible.
I actually wonder how viable it would be to claim to be a cylon right after the sleeper phase. In a 'hey, other cylon, whoever you are, executive orders me so I can use my once per game and reveal' sort of way. The best would be if you did that, were human, and got someone to executive orders you. And then you threw them out the airlock! Mwahaha!
At any rate... Do I think Sara should have revealed as her very first action? No, I don't. She hadn't had any opportunity to do any damage at all on her way out. She was Baltar, so she didn't have any good abilities to use (I think the cylon detector was broken), so maybe not? But sticking around for one turn around the table in order to cause a skill check to fail seems pretty reasonable. She was also president, so she had the potential to dig for 'brig you' quorum cards and she could make bad choices on 'president chooses' cards. The biggest thing, I think, is none of the other players had even had a chance to make obvious pro-human actions. There was a ton of opportunity for chaos and discord still. Especially with Byung and Andrew at the table. It would be a little different if I wasn't already revealed as well. Getting the first cylon revealed to slow the humans down a little and start using cylon actions is very good, and it doesn't cost you the chaos potential. So I probably reveal in her spot as the first cylon, but not as the second one. But the first chance I had to hurt the humans, I'd be all over it. (She eventually revealed to make use of her cylon reveal action, costing Andrew 7 skill cards which was pretty great.)