In the LTI-provider the options to fill in a profile field are very limited. You can only choose institution and place. There isn't an option to add all users from a published tool to a group.
It would be nice if there is an option in the published tool, to place users in a group and that User default values contain all custom profile fields.
Example case 1
Customer has a course and sells this to external parties. They can enter through LTI. The course as a discussion forum.
One of the external parties wants that their participants are separated from the other course participants. The normal way would be groups. Unfortunately there isn't a direct way to do this.
Example case 2
In the same course as mentioned above I'm using activity restrictions per published LTI-tools. Users from one external party have to do a test before they can start. This works really well with restrictions based on profile fields. Unfortunately the fields Place and Institution are already in use. And I cannot use custom profile fields.
Example case 3 (Moodle Workplace)
Some published tools needs place users in an other tenant. This is possible with profile fields. Yet again there are no custom profile fields to choose from.