UX designer here. I've learned that these changes are a delicate balance between allowing existing user to remain experts while improving the retention of new users.
This can be accomplished by making small changes over time that break up all the new info a user has to learn and avoiding the big UI reveal which people universally hate because all that new learning is required at once and they need to get stuff done.
Often times its required because as a product moves into mass market phase of its life cycle, it needs to be simple to use for lots of people, which mean it doenst work great for any specific goup.
Which is why I'm really in favor of allowing customizations to the user where appropriate. It allows experts to have control over their flow and new users can enjoy the UX optimized for them.
Meaning, if a new user is learning your software, how would they expect the next [flow] to go?
Consistency often shapes expectations but when things go how you expect them to, you don't need to learn new mental models.