Anonymous cash on the internet. Nobody knows who owns each bitcoin account so you can do all sorts of things you could not otherwise. It's very similar to (for example) Pecunix, although unlike Pecunix it's not backed by gold and it's distributed which makes it hard to take down. Anything black or greymarket is suitable for bitcoin.
100% legitimate uses? Well you could use it instead of Paypal and save a couple of bucks in fees but it's a lot harder than just using Paypal and there's no recourse if something goes wrong.
It's actually easier than using PayPal, in my experience. Just open your client, copy-paste the recipient's address, hit Send, and voila, done.
You don't have to create an account, add credit/debit cards and bank accounts, get verified, etc.
Definitely no recourse if things go wrong, but also no way for black hats to game direct P2P BTC payments either, like they can with PayPal's resolution and chargeback system.
It's only easier if you already have some Bitcoin to use. Converting money to Bitcoin takes more time and effort than just using your credit card on Paypal.
100% legitimate uses? Well you could use it instead of Paypal and save a couple of bucks in fees but it's a lot harder than just using Paypal and there's no recourse if something goes wrong.