Sorry, my mistake. It’s (more or less) the same as “Limit Superweapons” in some of the Generals mods. I’ve played them much more than the core game, and forgot that it’s named differently in vanilla ZH. In addition to limiting super weapons to one, it also limits super units to one in the case of Contra 008.
I am in general a fan of the rule, because it limits the viability of winning through pure turtling. I just find games won purely with superweapons to be unsatisfying to both win and lose. At the same time, it doesn’t completely remove them, and they are undoubtedly useful in breaking a tie. Especially so for the Tank General, since they lack artillery.
Not to mention that some generals (like Tank and Nuke) has extremely powerful research made available through their superweapon building.