Parts is a very useful tool, Groups is a very useful tool, but they are not friends.
If I am modelling a residential building, in which I use the Groups tool a lot because the dwellings are the same, I have to repeat all the work with parts in each copy of the group.
The only solution is to use links instead of groups, but it's not ideal.
Also when using parts for precast elements, which are repeated a lot and are the same, links is not an option, and plugins are not enough.