"STRICT ENCUMBRANCE MUST BE TRACKED OR YOU CANNOT HAVE A MEANINGFUL LOGISTICAL CHALLENGE."
- Not the DMG.
Apologies to Gary Gygax, whose "Meaningful campaign" quote has been much mocked but also much commented upon.
Encumbrance seems to be one of the issues that splits old-school gamers. Track it strictly? Track it strictly but come up with an alternative method, such as item slots or large items vs. small items? Come up with some alternative? Appendix O doesn't get the love that Appendix N or the Random Harlot Sub-Table receive.
I go with strict tracking.
In my GURPS games, in fact, in every one of my GURPS campaigns, encumbrance is tracked pretty strictly. On a 5-point strictness scale, with 5 being "by the book, always" and 1 being "who cares?", we play every game at either a 4 or a 5. Usually both.
I think this is because encumbrance is so deeply embedded into the core of GURPS.
Encumbrance is handled with a simple, concrete, real-world metric - weight. Bulk matters abstractly (hard to hide under a table with a halberd, say) but weight is concrete and tracked. Your strength (ST) stat directly translates to your maximum load. Just about all gear comes with weight. We routinely keep track of weight and I expect all of my players to be able to quote me their loaded weight (PC + gear) at any time.
Why I say it's the game system is that I don't really do more than eyeball my S&W character's gear. I didn't even think about encumbrance for my D&D5 guy. But GURPS, I know to the pound what people are carrying in their normal loadout.
We'll eyeball things and wing it a little in play - it's easy to say that you've got 60 pounds between "Light" and "Medium" encumbrance so adding on this treasure puts you at Medium and that's that, without doing the math beyond estimation.
Like I said, I think it's the rules. Since encumbrance effects so much (Move, Dodge, fatigue after a fight, penalties to load-limited skills, etc.) and the limits are so embedded into the system, and the metric for it is so common and easy to grasp, it's something we all track. No "200 gp weight for a scroll, and GP are 10 to the pound, but scrolls are bulky and have more encumbrance" to foul up tracking. No bulk-conflated-with-weight issues. You need to deal with bulk on its own, with a GM's judgement, but it's easy to get strict encumbrance tracking.
And so every GURPS game I've played, back to when we just messed around killing each other in Man-to-Man, we've known how much gear we're carrying. It's easy enough, and a big enough deal to not be a big deal at all.