Should You Break Out The Tiller?

The soil in my garden is rich and loose, not at all densley packed. Is there any reason to cultivate it?
That depends on what you mean by "cultivate". No amount of rich looseness will prevent weeds, so at least until the plants are large enough to be surrounded by mulch, you'll still haveto hoe (cultivate) to keep the competition from taking over--- unless the garden is small enough for you to hand weed.

But if you are talking about major soil disturbance like rotorilling, reson is on the sie of abstaining. The top 6 to 8 inches of healthy soil are filled with pores that allow the passage of water and oxygen, essential to the health of plants, and they also contain a great complicated web of life-forms that are eqaully important.

Tilling won't utterly flatten the pores or destroy the web, and it is just about essentail when you are incorporating green manure or breaking ground. But once the soil is loose, open, and fluffy, the less you do to ditrub it, the better.