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In Thingworx there are several services/functionalities that requires Adminsitrator group membership for user in order to execute them, for example:
1) Extension management
2) Import/Export functionality
3) Monitoring
4) Subsystem services
Is there anything else?
Jacek, to test this I would try to open Composer with a non-Administrator user and compare the available objects.
Let me know if this helps.