Which features are shared and which are separated between the accounts?

Groups: Groups that are set up for a sub-user are the only groups he can work on, and these are shared with the master account and any other users assigned with the group/s.

Tags: Tags are separated. Users can set their own tags. Users tags are not shown on the master account.

Reports: Reports are separated (unless its a user with Admin permissions). Reports that a user has set up are not shown on the master account (unless its a user with Admin permissions).

Saved Filter: Saved filters are separated. Saved filters that a user has set are not shown on the master account.

Custom templates: Users can use custom templates if the master account holder has made it applicable.
The user can also set new custom templates, which are not shown on the master account.