When is the best time of year to throw 3/4 oz. traps

Anytime you need to fish a little deeper than you can fish a 1/2oz bait. Late fall when you're trying to fish over deep grass or even winter time when you're trying to find the last clumps of live grass in deep water are both good times. 

Pre-Spawn!

When the fish want a larger bait than the 1/4 oz model.  I have seen it make a difference with schooling bass.