I was under the hood poking around and I found a vaccuum line with a large crack. I'm going to get it replaced, but I wanted to know what issues this causes. Will it drop performance?

 

it can, just realy depends on whats on the other end, i'm new to audis but long in the tooth as far as automotive, i can also tell you the hose is dirt cheap, and depending on location requires no tools to do your self

 

yes, more then likely will be connected to the diverter valve
etc, i had worn out ones on my car and that was the reason
i wasnt getting full boost with my new chip, so if you can, replace
them, will save you from future problems.