FAQ 2.4 & 2.5.
Whether you vote before or after you climb the mountain isn't that important, unless it's important to YOU. If you find the page is really good or lousy AFTER you've climbed said mountain, certainly vote accordingly. You could vote a 10 on the page, go climb the mountain, find out the page sucks and come back and change your vote. There's really no right way or wrong way to vote.
Most seasoned SP folks will/should vote on content and amount of information
. IF they feel so inclined.
On route pages, you can vote on the QUALITY OF THE ROUTE (stars) if you feel so inclined. This is NOT A VOTE FOR THE PAGE ITSELF, but for the ACTUAL ROUTE and what you thought of it.
Voting on photos is a very subjective thing so I won't get into that.
From my point of view, as an ancient SP contributor:
Voting helps devoted contributors determine what they need to do to improve their page and overall contributions. It's SP's measuring stick (although flawed) so content can be presented in searches comprehensively, such as by score, hits, etc.
If you're a lurker, if you could care less about contributions, if you're not that concerned about realibility of information, DMT's right. It matters not a hoot.
But Borut has the right idea. People like to be part of something, they like to be interactive in a community of like minded folks. SP is certainly that. Voting is one avenue for folks to be a part of SP without putting the work into a contribution. And for the contributors, it's nice to know when your hard work is appreciated, or when your work could be improved, too.
Like it or not, flawed as it is, voting does have an important part to play in SP's daily operation. If it's important to you, that's great. If not, then don't vote. That's the beauty of SP. It can be used to whatever degree that best suits the user at that time.