I have two teams, each of which defines at least one large (50-ish) group of team members. These teams have a lot of repositories (thousands in one case, hundreds in the other), access to which is controlled through the teams.
I recently attempted to change the default access for a group from Admin to Write.
This appears to have tried to generate one email to each group member per repository in the team - a very very big number. The operation failed after a long pause... it appears to have timed out while trying to iterate through generating those emails. The access on some repositories was changed, and others were not.
The users (who didn't need Admin access anyway), and our operations group, were not amused by the resulting flood of email notices.
Some way to manage this should be implemented; possibly: Provide a checkbox that selects whether or not email notices are generated for a change. You might want to send email anyway for any repo that a modified user is 'watching', but that's normally going to be a much smaller number. Generate a single email per user, listing all repositories whose access has been modified by a change.
I've marked the 'critical' because the present behavior effectively prevents me from making any change to the default access in my teams, and the current access rights are not correct.