I just recently started playing again after an 8 year hiatus. Maybe this only applies to us newer players, but I'm coming to the conclusion that I should throw fewer discs. For example, I only carry 2 midrange discs: Z hornet and Z buzzz. They both work for different shots. I've been tempted to buy a drone, roc, or even another buzzz, but at this point it's more beneficial to me to learn to throw what I have. After all, my bad throws are primarily due to "operator error," not throwing the wrong disc. After throwing only these two discs for midrange shots, I've noticed a major improvement in my midrange game.
As far as distance throws, I also feel like it's good to get comfortable with a certain set of discs. On the course, I almost always throw just a couple off the tee for distance shots (usually a Z nuke, glow destroyer, Z predator). When I'm practicing, on the other hand, it's nice to have some others simply so that I don't have to go retrieve my discs quite as often.
In short, I think it can be a problem having too many discs if you don't learn to throw them right. But maybe this only applies to us newer players...