For a long time I loaded every possible combination of bullet & powder I could get my hands on, for each gun I had.
While this gave me a lot of options, one thing it also gave me was a near certainty that whatever ammo I chose to shoot would not be what that gun was last sighted in for.
Then one day, the light bulb finally went off (dimly) and I realized that settling on, and sticking to one load was a rather beneficial thing for most of what shooting I do. Especially with handguns. And most especially with fixed sighted handguns.
I'm not a "one load to rule them all" guy, or at least not with everything. But I've learned that in my situation, for some guns, one load is all I need, or want.
For one example, the only load I've used in .45 Colt for the past 40+ years had been a 250gr bullet (usually SWC) over Unique, loaded to just kissing 1100fps from my Ruger Blackhawk. I've shot many thousands of those over the years, and I know exactly what it does, and at what range. I know exactly how to sight that gun, with that load to hit anything I want to hit out to 200yds without needing to think about it.
My Dad, who didn't handload, only shot one bullet weight and brand from his .357, it was Winchester 158gr "Lubaloy" and he rarely missed even very small targets.
The old saying "Beware the guy with only one gun, he probably knows how to use it!" applies also to the guys who only shoot one load from their gun. They generally know how to use it, and use it well.