I will admit, that most of the time when we have done it, it was because we had a young child. Generally less than 4, and they weren't going anywhere or doing anything without us. It was no problem if they were under 3, because Disney allowed infants up to 3. But we just didn't see why a few months one way or another should make a lot of difference, especially since they were taking up no more room than they had at less than 3 years old.
But, let me also say, that we almost never did that. We usually have either traveled with 4 people or 8 (including the children), so we have usually stayed in a 2 bedroom unit, or 2 studios or a 2 bedroom condo. We are going to Disney World in October and will have 9 or 10 people, total. (
Probably will be 10, including one child that is 3) but we got two studios at Poly because they hold up to 5 people each.
Here is our typical travel pattern, just over the last year or so (we have up to 12 of us who travel, but rarely more than 8 or 9 at a time):
Disneyland in July we had a 3 bedroom condo, 9 people. Disneyland in April, a 2 bedroom, 8 people. Disney World in May and June, 8 people, 2 hotel rooms on one and two Studios on one. Disneyland last November, 2 studios (at Grand Californian). Disney World last October, 2 hotel rooms. Disneyland last August, 2 bedroom Condo, Disneyland July 2017, 2 studios. Disney World a year a and a half ago in May, 3 hotel rooms.
As you can see, we travel a lot, I spend a ton on hotels, condos and
DVC (which is why I have over 1000 DVC points, and 28,000 timeshare points with Worldmark [Worldmark is one of the better Timeshare Companies, but I SOO MUCH prefer DVC]) so, maybe I'm wrong, but I haven't felt bad if we pushed the boundaries
a little bit, once in a while.
I'm not saying it's right, but, again, I'm sure there are lots of people who have done it. And, you will notice that I pointed out to the person who posted, that they were WITHIN THE CARRYING CAPACITY FOR THE ROOM, so, since the didn't have extra people, they shouldn't feel bad about rearranging the bed space. At least that is my opinion