More generally, it is good to think about the email notification feature as there are definitely users of it, and experiences that might not seem all that problematic (or totally problem-free) on-site could sometimes be more problematic when in form of email notifications.
For example, during one of the level solving contests Minim hosted, I sent a lot of PMs (and many around the same hour or so IIRC) for every little tweak to the solution and didn't think much of that. But then Minim made me aware that each such PM was also going to be an email in his inbox, as he is using that notification feature, and while ultimately it's not a huge deal it was also obvious that I should've been more restrained in my PMs (eg. batching), had I been aware of what's happening.