My educated guess is that 0.01% of all sent emails get an auto-responder response, 80% of that is from the recipient being out of the office. 

They all have some version of:

Thanks for your email! I’m out of the office from Monday, October 15, 2018, at 9:00 a.m. ET to Monday, October 15, 2018, at 5:00 p.m. ET. I will have access to email while out of the office, but if your email needs prompt attention, please forward it to 

I just got back today from being out of the office for 10 days or so. I also had access to email but didn’t respond to a ton of it. I didn’t feel any particular need to let people know that I was out. Email is already very asynchronous and the expectation is already there that a response will be sent when it gets sent. For me, urgent matters are rarely if ever conducted over email. I almost enjoy taking my time with email, enforcing that expectation. 

But in an informal poll (asking my wife), she totally uses vacation auto responders. I didn’t get a chance to dig in too deeply as to why, but I still am curious. Is it because people want to set a clear expectation that normally they are very fast with email, just not right now? Or it is just kinda whatcha do?