Oftentimes, the brown, dead-looking branches are not dead on the inside. The warm temperatures of spring will stimulate new growth in many of the dead-looking branches. If you prune your plants too early, you may be removing live branches.
2.  In general, pruning stimulates plants to produce new growth. Many gardeners make the mistake of pruning too early before the threat of cold temperatures has passed and then a period of freezing temperatures occurs, which not only kills the new growth but can even result in the death of your plant.
3.  The brown and crispy stuff actually protects the interior and sometimes the lower foliage of your plant from further cold damage.