I always forget that encumbrance in BX is an optional rule. I use it so often in my games that it seems integral to the system to me. I can totally understand someone choosing to "hand wave" the whole thing though.
It seems that encumbrance is one of those mechanics that RPGs tend to struggle with. Despite the simplicity of the idea ("Carrying lots of stuff is hard!"), different games have tried all sorts of methods to represent this. More often than not, they come up short, either in playability, or realism, or both.
The B/X method –being one of the oldest– is fairly simple compared to some, and while far from perfect, does the job well enough, IMO.
Two of the most commonly cited "weaknesses" of the mechanic are:
- No Strength modifier for carrying capacity.
- 10 coins per pound is a harsh scale.
The first is easily house-ruled. I commonly allow a character's STR adjustment (to hit/damage) to alter the allowed weights by 100 cn per ±1. So, for example, an 18 STR can carry 700 cn without being slowed down, while a 3 STR character could only carry 100 cn before being encumbered.
The idea that an individual coin weighs 1.6 oz. means you're talking some serious metal discs and a LOT of gold per piece. It's easy enough to explain away though; a relatively primitive society, lots of impurities in the alloy (a "gold piece" would probably be more like 10K than 18 or 24K), etc.
One tidbit I like in the system is the idea of armor slowing you down regardless of weight. The very fact you are in armor limits movement, etc. It tends to make PCs a bit slow. When you love resource management and wandering monsters as much as I do, though, that's a feature not a bug! To me, it's as much a part of the challenge as fighting monsters when players need to sweat running out of torches, or the extra time it takes to move through an area, because of all the stuff they are carrying or wearing. Watching them debate taking that one more sack of coins but leave their rations behind? Priceless!