All contacts added to a sub-group should automatically be added to the parent group – or include an option where the user can choose for this to happen automatically.

Subgroups make it easy to sort contacts within a group – but the process of adding contacts to (sub)groups is time-consuming and requires you to manually add them to both sub-group and parent group. When managing thousands of contacts, this quickly becomes a challenge. It would be great if adding someone to a sub-group (e.g. a particular industry within a “clients” folder, a particular school within a “former classmates” folder, etc.) would also automatically add them to the parent folder (“clients” or “former classmates”, in the above example). This would allow sub-groups to act more like filters within a group, given that filtering by things like industry, school, etc. is not yet available – and that users might have their own needs or ways of sorting people.