I guess this question can be answered by "Do whatever you feel comfortable with"

If you strip it back to the basics your idea goal is to not unbalance the car on the downshift. If you think that by "blipping" the throttle just before you let the clutch out works for you, keep doing it.

I personally do not do it. I brake in a straight line keeping it in that gear until the very last moment. JUST before I start to lift pressure off the brake pedal (just before) I will select the gear that I need for the corner. This way my road speed is at its lowest and if I make a little boo boo it should not have too much affect on the cars balance.

My method may not work for everyone, I am in a street car with synchros, standard box and twin plate clutch.