Massage is good for improving circulation, helping get rid of metabolic wastes (by products of being alive) and toxins, can promote a feeling of wellbeing, and a good therapist can do some little tricks on your muscles to get them to let go of the knots and tension that you have. It has tons of benefits.
Massage is probably the most primative form of medicine...think about it, when you fall or hurt yourself what do you do?? You rub the spot you hurt. If you are a child and you run to your mom with a boo-boo, what does she do? She rubs it and kisses it. Massage is really important at a very basic level.