If you are using the Planning Templates file with multiple clients, it is permissible to perform a "File>Save As" and save a separate file under each client's name on your primary computer, such that each client has a dedicated file for your convenience.  Populate that client's respective file with their data, and revisit that file as necessary through time to update their numbers as needed.

Planning Templates are just that: simple yet comprehensive and easy to use templates that help evaluate and clarify where clients are, and where they need to be. I recommend them highly.
— A.V. Martin Garneau, CIM, FMA, CFP®, PL.FIN., Canada