From a Distro point of view a new user need to be in some groups like video , audio , network 
and so on.. to have working thing.

Right now we can have an default user or an admin one.

This is because accountsservice just define 2 types of users:

 ACCOUNT_TYPE_STANDARD
 defaults taken from useradd -> group users

ACCOUNT_TYPE_ADMINISTRATOR
taken from internal default wheel or taken form command line at compile

Without a way to modify the user users with just groups 'users' can't do much in any kind Distro.

This could be fixed in 2 ways:

1) offer a option to modify users and run usermod on these
 hacky right now since you need offer a UI option to put the user in groups a , b ,c
 run accountsservice default and run usermod on the user..
2) get an patch ustream to allow additional groups for  ACCOUNT_TYPE_STANDARD

3) a mix of both :)

Reproducible: Always

Steps to Reproduce:
1. add some user with user-manager
2.
3.

Actual Results:  
User has just users as group or user+admin group without a way to modify

Expected Results:  
option to add users with other groups