I learned to fly RC models on mode one, my instructor had the knowledge to fly both modes but it was his preference to fly on mode one and also used to teach to all newcomers to fly on mode one.
I moved and stud away from the hobby for about 3 years, then I went to the local field and found out that every one flew on mode two, I did not much questions and I relearned to fly in mode two, why? My guess was simple, if for any reason I would need help from any other guy at the field when flying my models; I wish this guy could have the abilities to maintain the plane in flight.
I did not forget how to fly on mode one, it is simple for me, even though I have to get acquainted every time that I need to do it (not often).