I'm curious about the folllowing question, maybe some armchair economists (or sociologists) can comment:

Does the marginal advantage of an airline joining an alliance increase with the number of airlines already participating in the program, or decrease as more and more join?

Personally, I have two lines of thought -- first, given a finite number of airlines, if you were to divide the pie in half for example (or almost in half), it would be very important for an new airline to join one of them. I.e. anyone not belonging to one of the halves is at a great disadvantage.

On the other hand, each member of the alliance must offer increased services to passengers -- which may or may not outweigh the advantage of joining in the first place.
So, is it better for an airline to join an alliance when small, or large? Is there a size at which an alliance begins to defeat the purpose for which they were created?

Complicated -- just wondering if anyone else has thoughts on this?