NO, don't unclip during a descent! That really increases the chances you'll lose control.

Covering your brakes is good; feathering them when you start getting beyond your comfort zone is good; riding them until your wheels lock and your tires skid (another loss of control), or until your rims heat up and you lose braking power, is not good.

Do a search on descending, there are lots of good tips on the forum.