As your freelancing and studio work progresses, you eventually will have a body of work that you'll be able to pull from in order to woo potential new clients. There is a tendency for all of us to show our entire body of work. This gives the impression of more experience and a wider variety of work, so that potential clients from all areas will be more likely to choose you. However, is that what you really want?

I'd be willing to argue that it'd be much easier to get the same work by focusing within a certain area, as opposed to trying a little bit of everything. Not only does it make your job easier (albeit a bit more monotonous), but being a specialist, you'll be able to ask for more money in many situations. Of course, if you specialize in something you enjoy, then it's an added benefit.