I believe I understand most of what is going on in Groups, or I'm
confused and just think I do. :-)
The big difference from Clubs is that you can receive and send message
to the Group via eMail instead of doing it on the board itself. You
can still post and read directly on the board. For those that are
members, you can configure your membership for how you want to read
the messages. (this sometimes doesn't work the first time)
Since eMail can be in the loop the order of the messages can be
different from what you expect. If eMail is in the loop messages may
get lost. If you post directly on the board it should be close to the
same as the Club approach.
YaHoo servers overload regularly and cause problems that can add to
the illusion of confusion.