A Campaign Group allows you to consolidate similar Campaigns into a centralised, top level location.
At Campaign Group level you can manage daily spend by allocating funds to the group and setting caps to limit the daily spend across all campaigns in the group. Once the daily cap is reached (i.e. $500) all Campaigns in the group will stop receiving traffic but will not be paused or expired. Once more funds are allocated to the Campaign Group the campaigns will start receiving traffic again and generate spend.
Organise Campaigns into Campaign Groups per Geo. This allows you to monitor the activity of the different offers you are running in each Geo and see which perform best. This also helps to manage funds as minimum bids are set at a Geo level.