It also greatly depends on the context. Something like BugHerd (we use and love BugHerd btw!) I definitely want individual notifications for my errors, because

It also greatly depends on the context. Something like BugHerd (we use and love BugHerd btw!) I definitely want individual notifications for my errors, because as you already mentioned, looking at just the subject lets me know its priority. However, for something else that is less important, and likely more noisy, aggregated notifications are ideal. On our platform, our big feature is forms with routing and approvals. When a form is generated and sent to the organization's users, whoever is assigned to approve the forms would be inundated with submissions if they were not aggregated. They're not time sensitive, so acting upon each submission as they happen is never a concern.