Purpose of GNOME online accounts?

Folks;

is there some sort of documentation, howto, ... outlining how to make 
meaningful use of GNOME online accounts? By now, just out of curiosity, 
I did set up my Google and some other accounts in there, wondering 
whether this changes anything, but so far it doesn't. Evolution doesn't 
obviously see my Google Mail, the calendar does not see either my Google 
or my ownCloud calendar, the only thing I have seen so far is a link to 
ownCloud in Files which however seems "just" WebDAV. Can I use GNOME 
online accounts for more? Is this behaviour configurable, in example to 
sync files between server and local machine like the Google Drive or 
ownCloud clients do?

TIA and all the best,
Kristian