There are many, many heroes in League of Legends. Quite a few of them are fairly interchangeable but fill a specific role. (Annie and Veigar cast very different spells and play quite differently but when it comes right down to it they're both characters who specialize in doing burst magic damage.) Right now I haven't purchased any of the heroes so I'm stuck playing one of the rotating free ones every week. I can't specialize in a single hero but I could specialize in a hero type if I wanted to. Do I want to?
The advantage to doing so is I might actually get good at doing that one thing. Last week I played a lot of games with Warwick. He's a hero who fills the 'jungler' role on a team. Junglers don't gain experience the normal way. Instead they run around in the 'jungle' and kill neutral monsters that spawn. This means your team as a whole gains more experience and thus should outlevel the opposition. In big fights he can either be a tanky melee DPS or a straight tank who lacks a taunt. I was starting to get a good feel for how that worked and think I was doing pretty good by the end of the week. I just played a game today where I was laning like normal instead of jungling (Warwick is gone, after all) and I did a terrible job of it. I'd lost the feel for last hitting the creeps properly. I'm sure I'll pick that back up in a game or two but it does show the advantage to specializing. If I'd found a jungler in this week's lineup I could have continued doing similar things as last week.
The disadvantage is I get stuck playing a select few heroes. There's a lot of variety and I'd like to try them all. Also, what happens when my randomly selected teammates want to jungle instead? Do I say screw the team and play what I want anyway? Having the ability to fill in the gaps around the heroes they pick is very useful.
Maybe if I had a preset team I normally played with I'd be happy specializing in a couple heroes that fill the same role but for now I think I need to spread out. So this week I'm probably going to play Ashe and Annie and see how they work out.