There are many reasons why you should use Apollo. The main one is to improve your team productivity.
Invite your co-workers to any task or project and grant them special permissions, if needed.
External companies can be a great help to complete your project. Invite entire teams and customize different access levels and permissions for each external user.
There are no per-user fees. No matter what plan you subscribed to, you can add unlimited users to your projects.
The entire team shares the contact list, but contact tracking and collaboration on cases and deals can be enabled on a per-user basis.
Furthermore, you can grant specific permissions to co-workers on specific tasks such as billing, upgrades, downgrades and so on.