I need to uninstall SP2 in Windows to install a certain app. What exactly are the disadvantages of running Windows without SP2?

Less "security features" and no built-in firewall. The former point is rather worthless since there are always going to be security holes in windows no matter what you do, and the latter is worthless if you use 3rd-party stuff. Of course, more and more apps are requiring (or recommending, which means it doesn't much matter either way probably) it to be installed.

Of course, these are just my uneducated statments. I could've skimmed over some important feature or issue that was addressed, but I don't think so.

[rant]
From my point of view, SP2 is worthless and I've strangely had problems updating to it on every instance of windows I've installed. Whenever my obligatory next-install of Windows comes around, I won't be updating again.
[/rant]

OK goodbye SP2.

Well...New Games don't run good without SP2. Mostly because of stuff like dtntfx or netframe, their new versions require SP2.

That's no problem. I'm not a game freak.