The reason I prefer to transplant is that it promotes more efficient use of the soil space. Roots seek their boundary at the edge of the pot and then mass there, leaving alot of unused dirt in the middle of the pot. When you transplant, you encourage a stair-step structure in the root mass, causing the roots to be more evenly distributed in the pot.

To add one more thing though, as a *commerical* grower I probably wouldn't use pots at all, but that wasn't the question.

Dboy