Our philosophy is F15-F30, and F15-F25-F40.
Theory:
Using F30 on route to F40 might lead to F30 landing,
where F25 will not lead to F25 landing (hopefully
).
The use of F25 as a transition flap makes things smoother, and easier to keep yourself away from max F40 speed in speed unstable weather conditions.
I've thought that would be a good way of doing it as a well. I think I'm going to bring that one up.