When you edit a role to add new user or groups, the page will show all the selected users and groups without pagination.
Even this not being a problem for most of the sites, if a customer has a lot of users - let's say 19.000 - the page will take a long time to load what can be really annoying.
Maybe the best solution here would be to add pagination to roles page, allowing the users to be limited by a smaller number of entries.

Please check attached image. This problem happens to all versions of eZ Publish.