It's a good question, so I vote for your question too.
Here is the short explanation.
I guess everyone in DC would love to see qualitative articles, questions, and answers.
Voting is the way for us to introduce mechanism on DC which would encourage the creation of qualitative content and discourage the low-quality staff. And "Rating" is the sum of votes.
It's also the way for an OP to know how many people said "Thank you for your post and hard work" for his article. We can see articles with more than 10 "thank you for your post" signs.
It's the way to "Agree" and "I like it" for the answers and comments.
Also, sometimes Votes is the way to say "I disagree" and "I don't like it" and yes, it can be confusing to distinguish when you "disagree" or "dislike".
It's not an ideal mechanism, maybe we would introduce something better, need your advice here.