Unlike a single file line where each person in line is to be accommodated individually, a line for a character meet and greet is actually a placeholder for a group, as long as that group stays together when it comes time for the greeting and photos. Much the same way a line at a restaurant would work. If you go to a restaurant that does not take reservations or hand out buzzers, one person from each group must hold the place in line. When the one person in line makes his/her way to the podium, it is time for that group to be seated and the rest of his/her group can then rejoin them and head to the table. This way, the line might have 15 people in it instead of 60. It serves no purpose for all 60 people to form the line. The line gets too big and is inefficient and I've never seen an argument that suggests that at a restaurant, every man, woman, child and grandparent must stand in line accompanying the one person who is holding their place.
The only thing that matters (although it seems that some element of human nature can't seem to adapt to this), is the number of groups and people who are legitimately ahead of you, and how much time it will take you to get to the front of the line. You can try to crunch the math all you want, but the honest truth behind all of this is that if there are 25 groups ahead of your family totaling 100 people, your wait time will be exactly the same if all 100 people must wait in line without splitting up or if only 25 placeholders are in front of you with the other 75 people close by but out of line. And if you are the 101st person in the scenario where everyone must stay in line, then you are 50-75 yards away from the front with a view of nothing. If you are the 26th person in line, you are only 15 or so yards away from the front and have a view of the action, which in and of itself is a positive. All of this works as long as groups participate in the M&G as one group. You can't have one person save the place of more than one group. And it doesn't matter if the group has two people in it or eight, or if the group is a family with kids or a group of college kids. Math is math irrespective of the demographics.
Just consider this scenario. Your family arrives at a M&G line and there are nine people in front of you. The first person in line walks back to you and says: "Just to let you know, my group has six people in it. They are right over there, and when it is my turn, they will all join me at the M&G". The second person in line walks back to you and says: "I am in line holding a place for myself and my husband. He is right over there. He will join me when it is our turn." And so on, all the way through the nine individuals who are in front of you. You do the math and count that there are 47 people in front of your family. You could do one of the following two things. You could tell the rest of your family to get out of the line and go hang out nearby. Get a drink. Go to the bathroom. Buy an Olaf stuffed doll. Whatever. Or you could stomp your foot and demand that everyone in line in front of you reassemble their groups in line, pushing your place in line 30 yards further back into who knows where. What possible purpose would be served by doing the latter? You aren't going to see the characters any sooner. You aren't changing anyone's place in line. And you are preventing the 38 people who were not in line (as well as the rest of your family) from relaxing and enjoying the next 20 minutes while they wait. And you are denying WDW some revenue that could be generated by having people spend money instead of waiting in a line. Simply put, having everyone wait in line is the height of inefficiency all the way around. And this is not anything new. When people wait in line to check in to a hotel, one person stands in line and checks in while the rest of the family hangs out in the lobby. No one insists that a four year old be made to wait in a hotel check-in line. Ever. When people go to the movies, one person gets in line to buy tickets for the whole family. Perhaps another family member gets in line to buy popcorn. There is no social injustice in not insisting the the entire family weave through the velvet ropes to buy the tickets (or wait in line to use the self-serve kiosk.) One person acting for the group is perfectly normal, acceptable, and most importantly, efficient.
