Perhaps it depends on industry and position, but in my industry, there is no such thing as logged off or not present. I'm an exempt K-1 employee/owner and can honestly say that I do not recall ever being completely unconnected, even when I was W-2 and at the bottom of the totem pole. And once Citrix, blackberries, and then the true smart phones came along, it's only become more difficult to unplug. Now it's virtual offices and VDI cloud computing, along with handheld devices many times more powerful than my first work computer. I used to call my voicemail from a pay phone and check my messages, and now all my work voicemails are emails with WAV attachments.
Or perhaps it's easy to unplug, depending on how you look at it. It doesn't matter where I am - I can take a call, answer a few emails, and go back to whatever it is I am doing at the beach, or on a ski vacation, or wherever.
It's a blessing and a curse. I can go, but I'm never gone. On balance, I've rationalized that it's better than not going. And as often as not, the ability to check in and see that everything is fine and that I am not needed brings a feeling of relief and better relaxation. In return, the nagging feeling every couple of hours that compels me to look at the phone or iPad or open up the laptop can suck.
I expect my exempt employees to do likewise. I don't care where they are, but when I need them, I expect an answer within a reasonable time, barring issues like honeymoons and maternity leave. That doesn't mean I need emailed work product at 10:30pm on a Saturday. But if there is a big issue or important client matter or some other issue that I inquire about at 7pm on a Friday and I don't have an answer until 830 am on Monday, heads may roll.
Bottom line, if I'm doing it, they can too, or they can go work somewhere else. And I do my very best to not ask of them anything I would not do myself. As one example, I worked all day on Labor Day this year because I was not going to mess up two employees' vacations with spouses and families, so I did it all by myself and met my family for dinner later. In return, I expect similar sacrifice as the need may present itself.
I think the people I hire like the autonomy and the lack of "facetime" expectation. But with that autonomy and freedom comes responsibility. Some can handle it and some cannot.
I'm ok with that.