I have found the best time savings is when I buy factory made ammo.
Otherwise, I only reload multiples of 50 rounds of the same caliber at a time so that I can go through common stages without changing out equipment parts. All 50 brass stay together from when I start using them brand new, to when I eventually scrap it all at the same time due to it failing in some manner - usually loose primer pockets. If I screw up one by doing something wrong while reloading, it stays with its casemates to rub my nose in my error with one or two brass that cannot be reloaded. This used to happen more than it does now so most boxes stay at 50 usable brass.
So, if for example I am reloading .308, I will generally reload 300 to 350 rounds once I get to 50 or 100 rounds remaining. Each box of 50 could be at various stages of its lifecycle and based on the number of times shot and some measuring, I will do different things to all of the 50 empty brass in a particular box. ie If one needs body sizing, all 50 get body sized, all get neck sized, de-primed and shoulder bumped regardless as I only have my die set to body size and barely touch the shoulder. If one needs trimming to length all 50 get trimmed to length. If I notice one with a split neck or other metal fatigue defect, all 50 get turfed. Then it is time to prime. If one has a loose primer pocket it gets de-primed and the neck crushed with a pair of pliers. This is the last time the remainder get reloaded, the whole lot of 50 get turfed once they are fired. Yes I MIGHT get another reload or two out of the rest of them, but the signs are there and it just isn't worth a potentially serious problem. Then it is charge a lot of 50 of them and seat bullets to keep the powder in the case. I used to do a 100 at a time but found that I would manage to inadvertently bump a tray somehow and there would be a patch of little grains rolling about on the reloading table next to the loading block. So I now fill 50, check each one with a flashlight just to be sure, push a bullet in with my fingers as tight as I can to 'cork' it up and move to the seating process. Repeat the process 6 or 7 times until I am done with that caliber. That's just my process.
It might not be the quickest, but it makes high quality ammo that actually goes pretty much exactly where you want. If you want spray and pray type ammo, skip the reloading and buy bulk surplus when it comes on sale.