You've posed an interesting question. The number of rods I actually use depends on what I plan on fishing for any given year. I haven't used my 7 and 8 weight Sage RPLs (both 9' long) in a couple of years as I haven't targeted salmon or steelhead recently, but when I do, those get used.
For trout on medium to larger streams/rivers I use my 9' RPL which I had custom made back in 1990. It is my favorite rod and I have a couple of new, in the tube backups just in case something were to happen to it. I use it for chucking streamers, large double or triple nymph rigs, and hopper/dropper combos. It is also my go to drift boat rod and will always be in the boat with 2-3 additional rods--generally a 3 weight (sage 8'9" SLT) and a 6 weight (sage 9' rpl) and possibly the 7 weight if it's a big river and I anticipate the need to throw large streamers into wind .
For smaller streams, I use the 8'9" SLT which enables me to throw double midge rigs or dries, depending on the need. This is my go to rod for the bishop area.
For SoCal locals, I use a 7'9" Forecast rod I made up 3-4 years ago. It can throw double nymph rigs (smaller nymphs) or dries.
I'm not a real short rod proponent as I like to mend my line a lot while drifting, and frankly have found that the shorter rods just don't do it for me. I've had them down to 6' but now the shortest rod I own is 7'6", and it rarely gets used.
I have many rods that never see useage except in situations that might require something one of the above rods can't do. You might say I'm a collector, I guess, as I have somewhere north of 20 rods and south of 50 rods. Frankly I don't really know as they are strung out between Idaho and California, in storeage units and closets, etc. If my wife knew how many I had, I'd probably be looking for a new home.
Maybe I could live in Pete's rod making palace.
Actually one of my goals for this fall and winter will be to list and sell a number of these overflow rods(sage, winston, tfo, powell, loomis)
"Should you cast your fly into a branch overhead or into a bush behind you, or miss a fish striking, or lose him,or slip into a hole up to your armpits-keep your temper; above all things don't swear, for he that swears will catch no fish."