It's as simple as I put it below:
- Developer changes are saved as a part of your PDI solution.
- This solution should be then scoped in the tenant (which happens by default in the tenant in which you are developing through default BC content) which is only possible by Business Configuration wc.
- PDI users are not authorized to use to Business Configuration wc. If they need to lock BC, they need to do it from PDI itself.
- When a Non-PDI user (business user) is able to scope in solution and make it available to other Non-PDI users, you can obviously say that every other user should be able to use the solution developments from the point you scoped it successfully.
- It is always recommended to use Business User for testing solution functionality.