The decarboxylation with heat is what makes the thc potent when ingested.
When smoking, it happens on-the-fly from the combustion or vaporizer heat.
There's a chart in the archives that gives "time X temperature" for efficient decarb.
When you get it just right, there's a dramatic increase in potency.

At 100 degrees C. it takes a very long time.
Use a pressure cooker and you shorten the time needed.
If you will be baking with the butter, you can boil for a much shorter time because the oven's heat will complete the decarb for ya.
Ju's look up decarb in the archives. It's all there.

Aloha,
Weezard