Hi ukwndpthz, and welcome to the O.D.J.com family!
Lets see, there are many reasons why a keyboard is a good idea:
1) Yes, it just makes thing easier.
2) Some programs will wright the note you have chosen on your keyboard onto your piano roll etc. What's really nice is if you have touch sensitive keys, the velocity at which you hit the keys is registered on your computer.
3) Any effects that your keyboard has, such as resonance, cutoff, etc. can controll the effects on your PC too.
4) For the most part a midi keyboard is not NEEDED, but think of it this way: you can control and navigate your computers O.S. with only your keys, but when you add a mouse, you can do more, and do it faster.
5) I used to use a mc303 crapbox (I mean groovebox ) to act as the master for my setup, while things like rebirth were the slaves.
As far as buying a keyboard, if you just want it to control your PC, I suggest finding yourself a good deal on a used synth at a pawn shop. Just look for a midi model, and then decide from there what other features you would like. \
I hope this helps you ukwndpthz.