The first thing you should know is, that the votes come from a daily pool, so the more you vote the uselesser is each vote, so be carefull with that.
But at the otherside, of course you have to catch an usefull article where you also can earn from your upvote, so you have to think bothsides.
For example, if one person only votes one article, this article gets all his steemit power, so the article owner gets more paid.
so,it is important that you rightvote, and not spam with votes.
so ,if a user votes, 1000 of articles, and then votes yours, you will get less money from his vote for your article.
i hope i could explain that.