I'm pretty sure it is official Disney policy that line cutting is not permitted, and you can be removed from lines for doing so. If you don't believe me, try it in front of a CM.
My common sense tells me that the family in front of me is not prejudicing me if they are taking pictures and allowing gaps to form in front of them, whatever its size, as long as that gap does not delay me actually getting on the ride later than what I otherwise would have. In the TSM standby queue, as long as there are people held at the FP merger point, it doesn't matter if the family in front of me lets ten foot gaps form in front of them, then move all at once to fill them, or if they are constantly taking three inch paces never allowing more than twelve inches of space to form between them and the people they are behind. I will get to the FP merger point at exactly the same time.