In the Spring, I re-pot my rosemary. Historically, I've moved it up to a bigger pot, but I might not want it to get any bigger at this point, so this year I might root-prune it (and prune a similar amount from the top) and put it back into the same pot.

I do usually give a bit of fertilizer at re-potting time. I've got some stuff that's designed to be an organic "herb fertilizer," which I take to mean it offers some good nutrients, but not heavy fertilization. It seems to work well enough.

I think any plant that lives its entire life in a pot is going to need a bit of fertilizer now and again, because unlike plants in the ground, they have no ability to get nutrients other than what you give them. Just don't over-do it in the case of herbs.