Even today you are better off shooting manually once you have metered the scene.

Otherwise your meter will pick up on color differences in a given framing and meter slightly differently. Shots will be 1/30th of a second, 1/25th of a second, then thanks to the freedom of aperture priority you might get little weird 1/32ths of a second you don't have discretely on a dial. How about iso. same thing, one shot iso 200, another iso 250, 275 this other one. Oh this one went up to iso 800 and the meter cut the shutter speed. Aperture too. This one f2 this one f4 this other one f2.5. This wasn't such a big deal even in the full auto film era since 35mm film has such latitude where you can't really tell a couple stops over or underexposed.

All these shots, ever so slightly different from one another even if the lighting of the scene didn't really change.

Why does this matter? Batch processing. If I shot them all at same iso, same shutter speed, same aperture, and I know the lighting didn't really change over that series of shots, I can just edit one image if needed and carry the settings over to batch process the entire set of shots.

If they were all slightly different that strategy would not work so well. Shots would have to be edited individually or "gasp" full auto button which might deviate from what I had in mind. Plus there are qualitative trade offs too when one balances exposure via shutter speed, vs via aperture, vs via iso.