To play, you only need one...right? And much can be learned in a one disc round...
The biggest thing I learned by "discing down" (pulling high speed drivers out) and carrying 3-5 discs only is that it will force you to get creative and throw on different lines, angles, releases, etc.
It is easy to rely on a disc for this shot and a disc for that shot and so on. By trying to get one mid (your Mako, for example) to do as much as possible, you'll be forced to throw hyzers, annys, tunnel shots, slow turnovers, etc. Throw low for minimum fade shots, throw higher to get more, and so on. You come to the realization that you, the thrower, can do alot to influence the shape and line of the shot. You'll get to know that disc inside and out, and also determine if it really has the versatility you need.
Using understable discs for hyzers can give a really long sweeping curve that you might not discover if you always reached for the stable/overstable disc. And vice verse for really cool s-shots.
I used to carry about 20 discs in 15 molds. Then I did this minimal bag for a while. I'm down to 7 molds and feel that I justify every one. Even if I carry 20 discs now, it's still the 7 molds, the differences are wear stages (and weights for my putters) which I can use for additional shot shaping and wind conditions.
And it's still fun for me to head out with a Voodoo, Roc, and Gazelle and play...