Just wondering what the point is of the rule which says that a miss can't be called when a player requires snookers?

I'm sure there must be a sensible reason for it but struggling to see what it is!

Also, does the rule work both ways, so if for example player A needs snookers, can a miss be called against player B, or can no misses be called at all?

It becomes a free ball though, so that's even more useful.