I try to fish close to the bottom whether I am trolling or casting.  The exception would be trolling for trout in deep water.  Years ago I switched to braided line and would never go back to mono.  When I am fishing close to the bottom, I probably go through 20 feet of line a day due to abrasions and snags.  When trolling Rapalas I try to bounce the Rapalas off the rocks.  I recently purchased a spinning reel which holds 175 yards of 20 pound braided line.