Different Stars with the same set of dimensions

Hello,
I have the following question:

What should be done in situations where we have different stars with the same set of dimensions? Should they be joined? I mean to make a single star of them.
Why should we not join them? Other than the fact that they represent different granularity?

thanks.

It depends. Do you have a particular situation in mind?

For example:
A star records information about contracts process of employees.
Another star is about the cadre and scale (which may change in the tenure of a contract) shares the same dimensions. In this case we have two different stars.
If the cadre and scale of an employee would not change during his tenure, then we could join the stars and make it a single star. Am I right?