When you start adding Groups in One Community keep in mind that a good structure from the beginning will keep your CRM clean and easy to use in the future.
There for we advice you to work with Main groups and Subgroups. It works like a funnel. For example start of with a Main group called 'Events' then add all your 'Events' as Subgroups. In the single events add Subgroups like: participants, partners, volunteers etc.
! People and organisations in Subgroups will always be in their top level groups as well. This can be very useful when making Email campaigns or Segment. Sometimes you just want to send an email to just the participants but the next time you might want to email everyone linked to the event.