Coworkers, clients, and subscribers typically expect fast responses and solutions to their problems, particularly from people working in customer service, marketing, and communications jobs. Out of office messages provide them with a polite, concise, and professional explanation of why you cannot respond right away. You can provide an OOO message if you are gone for one day, one week, or several months.
Top of the iceberg though. Oh, and she also works with external contacts, including prospective clients.

My OOO is almost always “I’m out of the office and will be returning on x date.” My email sig has instructions along the lines of “for questions on x, email this list” for a couple of the more common areas people would contact me about that might need an urgent reply (as the lists go to more than just me, obviously), but most people have finally figured out to contact those lists to start with, anyway. If I were in the middle of a project or something that needed to be moved along in my absence, the project teams usually know when we’re out, but I’d put a back up in that case, if needed, but generally there’s not much to be gained by a longer OOO from me.
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).