Yea the tag will put on post is very important because that's what gives someone an idea of what your post is all about.

Yes it also increases the chances of you getting more upvotes in some cases but not all the time.

So your tags should correspond to what you are writing about.

And in steemit using some particularly tags like #surpassinggoogle,#ulog, and some popular tags increases your chances big time.

I have done it several times and it do work for real.