It was the same for those who did not have a good mastery over their transformations, resulting in them being unable to control them properly and being unable to take on their desired form right when they needed it.
There would even be people with that type of ability who would become so used to using a certain form or number of forms that they would forget about the others they would have available, causing them to forget about them and perhaps even struggle to use them later.
It was always good to practice that kind of ability since it was quite complicated.
The triggers and reactions needed to be learned and practised while keeping a record of such things would always be helpful toward not losing track of such important aspects of what they were capable of.
Shapeshifters were able to take on most forms, and in the case of Ash, she was able to take on the forms of those she used her technique on while they were dying.
