It's more for if someone sends an email out side of working hours.
If they send 2 email (one to create the ticket and one to update) we won't really know what there has been an update till the next day.
For example, first email:
Hello my phone isn't working, no rush but can someone check this out?
Email 2:
Sorry turns out this is urgent and needs rectified ASAP.
So we won't know that this issue has now turned urgent unless one of the agents log in.
Although the email is outside working hours, we do generally help our clients out of the issue is urgent.