Out of office messages are important because they let people know you are away from your regular work duties. These messages help businesses and projects run smoothly when a member of their team is away. They let people know you received their message and will respond by a certain date. This helps prevent confusion and frustration if someone is trying to communicate with you by email but not getting an answer.
Hah! Maternity/parental leave is often 1 year here, so there is zero expectation you will read or “catch up” afterwards. We keep our email addresses during where I work (Canadian government), so it’s standard to put an OOO that just says “on parental leave. Please contact X instead” with no reference to actually reviewing any of those emails, and often not even a projected date of return since people often flex their return date or take extra time, or just return to a different position entirely (out of choice).

I mean, sometimes I put up an OOO because I’m on vacation and not checking email. Sometimes I put one up because I’m travelling for work and will only have sporadic access to my laptop, but might get to check once or twice a day. In my role, it’s important to make that distinction. Maybe it’s not so important for other people.
A client rings to tell you your out-of-office message has a typo in it, or, worse, is mind-numbingly boring. Suddenly you’re wrenched out of holiday mode and back into the throes of work, weeping as you log back into your email server to change your response as your shandy grows warm and flat.