What opportunities are displayed for My Open Opportunities and Open opportunities where I am on the team?

Selecting My Open Opportunities displays a list of all open opportunities expected to close within the current calendar or fiscal period where you're listed as the opportunity owner.

You're automatically the opportunity owner if you created the opportunity. You also can be assigned as the owner by someone else.

Selecting the Open opportunities where I am on the team list displays a list of all of the open opportunities expected to close within the current calendar or fiscal period where you're on the opportunity team. You're on the opportunity team if you created the opportunity or you can be assigned to the team either by an automatic assignment process or by another team member.