It's a staple of old-school D&D-- your party is wandering through the dungeon, and you see a door. What's behind it? Why, it's a 10x10 room, with an orc guarding a chest.
I never really thought much about it. For years, it was just sort of there. But this weekend, whilst painting my bathroom ceiling (whose dimensions vaguely approximate the aforementioned room), the thought occurred to me, to wit:
Let's be generous, and have the orc stand over the chest. Put them both in the corner. Now, orcs are what, 5 feet tall? Ish? And humanoid in shape, so they'll have an arm span of about half that (see the Vitruvian Man). Give them a short sword, and that's another 2 feet. So the orc, by itself, with minimal room to swing a sword, already takes up about a third of the available space (roughly 14 foot diagonal).
A typical human fighter is closer to 6 feet tall, and uses a long sword. So he will use up closer to half of the available space.
This means if the fighter obligingly wedges himself into the opposite corner (very gracious of him), the two of them will have just enough room to swing their swords at each other without overlapping. If they're using fencing foils, that might work out, but can you imagine an old-school orc fencing? Any sort of decent swinging/cutting hack-and-slash weapon and the visual starts to get a little silly.
And now that we've established that, here's the 64 gp question-- where, exactly, during all of this derring-do, are the wizard, the cleric, and the thief standing?! Out in the hall, I guess. Otherwise someone's going to be the recipient of an unfortunate elbow, if they're lucky.