Storage for the cheap or rarely used ones. Sacrificial wrenches need bent with a torch or cut/welded, so I keep a full set of combos just for that. Problem with upgrading is often your old stuff has such little value selling is hardly worth it.
IMO, if you're buying duplicates of the same item, like standard combo wrenches, you run into the wall about 3 sets. You can only use two of the same size at one time (rare), so that "justifies" 2 sets. The third needs a zip tie through the box end, and stored away. Once you get into various styles like.double box and ratcheting, IMO, 2 sets of combos is plenty, single sets of everything else. Now, if you have flex head ratcheting and straight fixed ratcheting, and fixed head angle/reversable ratcheting- those are 3 different tools. Whether it makes sense for a non-pro to have that level of minutia, that's a different story.
I bought a carry tool box from harbor freight to stick that kind of stuff in. 7mm 3/8 drive impact sockets, wrenches ready to die for the cause, etc.