I don't know, do you have an extra $0.83 per month? It's not really a matter of affording it anymore -- you can probably find offers that will get you domain hosting for free; I reference the cost of registering through Google Apps and using Google Pages.
If you want people to be able to find you, it seems like a good idea. If you want an e-mail address that you'll keep forever, it seems like a better idea.
As the cost approaches zero, I think the better question is: Why wouldn't you have a personal domain?Link -- here's mine (took about 5 minutes with Google Page Creator)