[Nickles]

The kitchen basically enables a user to easily customize their device, and 'upgrade' the stock ROM that comes with the phone.
The kitchen has a laundry list of programs that you check, or uncheck, depening what you want installed on your phone. Many of the items you need for basic functionality (like .NET Framework, MMS, Dialers. etc...)
but other programs can be omitted (like Office, Games, etc...) if you are looking to totally streamline your device and take total control of what you install on it.

probably the largest benefit of flashing to a new 'custom' rom is the developers (DCD, Nex, No2, Vet) go to great lengths 'crafting' these roms, to ensure they are fully optimized for Memory usage, battery life, bluetooth performance etc... basically, they remove most of the bloatware that comes packed on the standard stock rom..

so you end up with a much faster, more reliable device in the end.

the Kitchen just allows you to 'customize' this custom rom, with programs and features you want to 'install'.. and you are right, if you install them from the kitchen, you cannot just manually un-install them..
so be careful what you are picking, to make sure you really want it.
you can go through SEVERAL iterations of a flash before you have your device the way you want it..

if you are this new to it however, i would recommend you read the many threads in the upgrade forum first, to see what others are up to, and learn some tips on what NOT to do.