Long term, it is generally best for the gymnast to stick to one particular coaching style, one particular plan of progress, etc. It's great for them to occasionally go to a camp or a joint workout with another gym or work with a guest coach from time to time, but most good coaches have very specific progressions, and it's not beneficial in the long run for a gymnast to switch from place to place, because she never gets to follow through with the entire progressions as originally planned.
This reminds me of Marvin Sharp's story with Bridget Sloane. I remember reading something back when she won Worlds that basically said the same thing - he had a plan for her progression from day 1, and by sticking it out, she fulfilled that plan. Had she had a change in coaching staff as she started optionals, it would have thrown her off track. It was also somewhat in reference to why he didn't (doesn't still? I don't know) do TOPs at his gym.