Well it does, actually, because the day before doesn't leave much time to plan what you're going to see with others, or listen to acts that are playing during times when you've nothing on. If i've 3hrs of a gap, and several acts playing different stages during that time, it'd be nice to know now, so that I can give them a proper listen.
If I don't find that out until the day before, then basically I'm probably just going to skip the unknown to me/probably smaller acts that I would have otherwise had a chance to listen to and maybe see.