Why do I have pendant invitations to workgroups?

Someone invited you to join a workgroup. You must accept or decline the invitation.

You have been probably invited to a group after talking with this person about working together for a shooting or some related project. This person has created a workgroup to let all team members of the project keep in touch and stay up to date with anything related with the project. When joining a workgroup, you'll be able to talk with all the team members of the job, and even download files and photos related to it.