Users -> "User roles" setting,
There're 3 options as below and currently it seems that only “Default access to new modules” is used. I confirmed, with the help of the tutorials on the document, that it affects the custom frontend and the custom widgets.
The other 2 options do not seem to affect anything.

• Default access to new UI elements
• Default access to new modules  <-only this seems to be in use
• Default access to new actions

Referring to the official document, I think "Default access to new UI elements" might affect the custom frontend.
 

 
Do the 3 options work correctly or not?
Or, are the 2 options just for the future, which means it's just a documentation issue?