I mainly agree with Choxolate. I too have been in a group (of 12) and now have sole ownership. My experiences are:
1. Much reduced costs. Big plus.
2. Cannot fly exactly when you want and most certainly not 'at the drop of a hat'
3. Much more difficult to sell a share than a whole aeroplane. There is at least 2 members of my last group who cannot sell. I sold, but at a give-away price.
4. The aeroplane may well be left in a condition you don't like, i.e. empty or even at another airfield! Pilots sometime don't return on time, due weather etc.
5. Difficult to get everyone to agree to an upgrade or non essential repair.
6. Cannot sell the whole aeroplane unless a certain percentage agree.
7. Nice to fly with other group members . A plus.