Never liked the waste of product either, along with being at the mercy of what it was doing outside before I could go out and use a rattle can to apply primer. I also have no overspray in the room and can put primer exactly where I want it, so if anything needs to be masked off, its just going to be a small area around where I'm shooting the primer. Granted, the decanting process is more complicated than just shooting directly from the can, but the small can of Tamiya Surface Primer ends up lasting me anywhere from 4 to 6 months...and I prime everything.
Messing with different ways of getting things done has always been half the hobby to me too. Before I started decanting, I tried watching videos of how to do it, and there were all these guys out there putting masking tape over paper cups, punching holes in the tape, and decanting just what they needed right then. A bunch more were cutting the cans open, making all of these elaborate setups to keep from making a mess, and that's when I thought "there HAS to be a better way!"...and then the gears in my head start turning. I just bought a case of mason jars and started decanting everything, a whole can at a time. 5 to 10 minutes of time investment, for months of trouble-free, weather-independent airbrushing.