Try to get it as good sounding as you possibly can. Do anything that the guy who listens to it gets blown away when he hears it the first time. A good mastering sounds more professional as well, like you know how to deal with sound.
But noone would expect a perfectly flawless mastering, just don't send rough sound sketches and discriptions like "Y'now, when I'm finished with it and it gets mastered, it's gonna sound like this and that..." Unless you already are in contact with a label.
"In my life I widened a lot of holes!" (Jeff Milligan, talking about slipmats)