eDiscovery - end user's permission to edit the search query on the case but not to change the Location.
Nowadays, there are two roles in the Security & Compliance Center: eDiscovery Manager and eDiscovery Administrator. Both roles allow the search for information through keywords and the selection of the mailbox within which the search is performed.
Following the best practice of assigning the lowest possible privilege, it would be a great improvement to create a new role for the end user which only allows him to search the information in the mailbox assigned by the administrator.
In other words, that the final user could perform the search query feature but being restricted on the Location area.
Jason Cramsey commented
When assigning a user to a case, I would like to be able to restrict them to searching only the locations on hold in that case. Essentially just remove the All Locations and Specify Locations options from the new search form. I've tried this with the compliance search filters, but this will not work in our environment.