there's the chemistry issue You can be perfect in every way, but no attraction. Sometimes you feel attraction, until you kiss and there's nothing . Chemistry isn't predicable.
Compatible physical affection needs are very important. I don't' mean just sex, I mean cuddling, touching in general, kissing, hugging, etc. Some people like a lot, some people don't. If you're too different, you're going to drive each other crazy, or miserable. Since people tend to be more affectionate a the beginning of a relationship, it's kinda hard to predict if it's going to be right down the road after the hormones calm down. I think it would be too easy to get emotionally attached before you know some very vital things.