I wonder why so many people chose Strong Back as a must-have? Don't they know you get two pack mules that can each haul another 200+ lbs of junk for them? Load them and you up, then fast travel to town to dump/store/sell it, then go back in the field again. Putting off that inevitable trip just for another 50 lbs of junk- what a waste of a perk(s). Unless you are getting it for hardcoe, where every ounce counts... that of course is different. I don't care about having to eat/sleep/pee/fart in FO, so I sometimes forget about that aspect.
Strong Back comes in really handy if you're using heavy weapons and armor, and/or do not use companions.
hardcoe mode is also a factor, since ammo has weight, and some folks go even farther and have modded some normally weightless things like Stimpacks to have weight in that mode.
You're right that we don't absolutely
need it, but we feel the benefits far outweigh the opportunity cost of a perk slot. Myself, I often wonder why so many people take Finesse, since you don't need to be a crit-monster to be unstoppable in combat. Then again I'm not a fan of sneak-sniping either, so take that as you will.