The other day I mentioned that I run encumbrance strictly in GURPS, and that I think the importance it rates in the game and the ease of handling it (clear and discrete levels, real world measurement) encouraged me to do that.
In Swords & Wizardry, I said I just eyeball my gear and estimate. There is a pretty good reason for this. As far as I can tell, in S&W Complete:
- Weapons are extremely heavy (10 pound bastard swords, 10 pound spears, 2 pound daggers, etc.)
- Armor isn't exactly light, either (70 pound plate armor)
- Non-weapon equipment doesn't have any listed weights at all.
- A "normal" level of gear, not counting armor and weapons, is 10 pounds.
- We're playing a 100 coins/pound treasure system.
So I eyeball it. Non-weapon gear is a basically set amount of vague total weight for a nebulous amount of gear. Maybe to make up for that, armor and weapons are very heavy. My armor and weapons load alone puts me close to my 105 limit for move 12. Add in the 10 pounds and treasure and I go right to move 9. Move 6 is like 70 pounds away from my starting point, which is 7000 coins. Most of the time that's not what we're carrying around. Since my move can't ever go up to 12, and rarely (let's say never in actual play) goes to 6. So I don't track encumbrance. The game makes it not-important. It doesn't care so I sure don't either. (On the other hand, I have a five-digit XP total exact down to the ones column, and a treasure total tracked the same way. Those matter a whole lot in S&W! I bet most other OSR types have their XP total as exact as I do, too)
In D&D5, encumbrance is a little more detailed. But I found that my armor choice determined my move and encumbrance level rather more than anything else. So again, eyeballing it based on my very large gear choices. I don't carry a lot of assorted crud in dungeons (probably a smaller assortment of gear than the stuff I carry in my actual toted-to-work-and-play backpack, which is chock full of everything). So I could make an almost certainly accurate assessment of my load based mainly on my big combat gear.
In our AD&D days, tracking encumbrance was such a pain I think I started handing out Heward's Handy Haversacks and Bags of Holding ASAP so I'd have an excuse to not keep track. I still don't really get the whole coins-to-relative-bulk-and-weight thing. I mean, I understand the intent but I had to look up everything, and I don't think anyone really knew what to do with it all. We played totally mapless and didn't track torch burning times or anything, either, so movement rate didn't matter unless you were faster than human. We'd read about poor Dimwall and Drudge but we wouldn't calculate encumbrance. We might go as far as counting our load the first time we made a character, but it was quickly ignored in actual play.
This isn't to say I don't look at old-school dungeons that have a 10' pit with a dead thief in it with a sack filled with 3000 sp and leather armor and don't think "He was carrying 300 pounds of coins?" It's just that I couldn't tell you what leather armor did to your encumbrance level without looking it up each time.
I wish I could recall how we did it in Rolemaster. Maybe the wrong way, I can't recall. Maybe not at all, since it was basically my AD&D group, minus a few others, that made the jump. Same with most of the non-fantasy games - it's been too long, but since I can't tell you off the top of my head how encumbrance worked in Top Secret, Gangbusters, Star Frontiers, Twilight 2000, Traveller, etc. means we probably didn't pay attention to them. None of them are very gear-carrying-centric games, though, since you always had a vehicle around or got dumped on Volturnus with nothing.
But that's why I think the game system matters. The approach you choose matters, the effect of encumbrance matters, and if the game system doesn't think it's important, or makes it clunky to track, I don't track it. If it makes it easy enough, and important enough, I'll do it.