I enjoy shooting my 68# bow. I also find that I shoot better when I draw and hold, so I have to work to keep my strength up. A couple of years ago I made a couple YouTube clips (although I cannot for the life of me remember why) where I drew and held the bow for a count to 10 before releasing. I did one with heavy bow and one with the lighter (48#) one, but I must have deleted the clip with the heavy one.
I'm NOT saying that you should ever hold 10 seconds when actually shooting, but I think it's a good idea to be STRONG ENOUGH to.
Anyway, I find that my shooting is SOOOOO much better when my muscles can absolutely dominate the bow, heavy OR light. I've not been shooting much this year, so my endurance has waned, but I usually try to work out with the heavy bow several times a week, without even loosing an arrow.