How do Groups affect Access Profile permissions?

Group permissions override certain access profile permissions.

Groups give limited access users the ability to have specific full access like permissions. Group managers are given permissions to view Contacts, Jobs, and Tasks that are assigned to the members in their Group.

Normally, limited access users are only able to see the Contacts, Jobs, and Tasks that are assigned to them, but if that limited access user is made a Group manager, they will be able to also see the Contacts, Jobs, and Tasks that are assigned to the other members in their group.

For example:

In the following image, Gerald is the manager of a group, but has limited access. When viewing his calendar, he can see all of his tasks and the tasks assigned to the team members in his group.