sessionhash?
 

I've read about people COMPLETELY removing sessionhashes- mainly for targetted advertising with google adsense, etc.

if it can be completely removed, why is it there in the first place? what exactly does it do?

Its there so people can still browse the board without having to accept cookies. In vB3 the sessionhash only ever appears if thats the case, in vB2 it appears unless the user has explicitly stated they wish to accept cookies.

why, though? why would you need cookies if you're not logged in?

To track the users session, otherwise every page click they make a new session for another guest is likly to be created.

so if you completely removed session hashes that'd be the only result?

Any user without cookies wouldn't be able to do anything, other then login and be logged out again, and tracking of users who are not logged it wouldn't be possible most of the time, which could possibly decrease performance.

not be able to do anything..? meaning? what couldn't they do? they can still browse just fine, I checked that out myself..

If a user rejects the cookies and doesn't have a sessionhash vB won't be able to identify them, thus they won't be able to do anything.