I'm sure the spirit of the "restrictions" rule is that you don't want novice cave divers in a situation where one can't get to the other to share gas or otherwise help. But there are places like the Lips in Ginnie which aren't strictly restrictions, since you could almost certainly get two divers through them side by side . . . But in practical fact, it would be a bear, because the second diver would have to be in a place which is highly disadvantageous with respect to flow, and since both of you would be clawing your way through, being of much assistance would be pretty difficult.
On the other hand, the Rocky Horror passage in Madison (which looks like TONS of fun) is clearly exactly what we aren't supposed to get involved with -- a long section of narrow passage, where single file formation is forced by the cave.
I think it's sort of like diving tables . . . You can be absolutely black and white about it, and obey the absolute letter and spirit of the rules, and maybe as you get a little more experience, you can actually start to evaluate what you're looking at with respect to what the limitations on your skills are and what the restrictions on your cert are supposed to do for you. Me, I'm still at the pretty black and white stage of things . . .