@Sevenlayermuddle - now there you have got me. Simple answer is none, yet. But technology changes and new opportunities keep catching me out. So intentionally making it completely over the top as I don't want to have to redo things. No idea what things will be like in five years or so. So guilty as charged sir.
If I had to guess about the future, then my guess might be sync or some kind or backups across the LAN. Backups have been a nightmare all my life. Storage servers. I would like to park some kit in the wrong building because of fire.
When I had a terrible house fire in 2003 I would have lost all my main computers and all my data had it not been for the good fortune that they were not in the house at the time. I had moved everything to an office in Broadford then because of catastrophic building work renovating the entire house so that is why they were not there when the fire broke out. On the day of the fire, I was on the mainland with Janet recovering from surgery the day before. When I got out of hospital a week later, Janet had been to Broadford and had got my main server out of the office and out it in the back of the car, with a keyboard, mouse monitor etc. and she then drove the gubbins and patient down to my parents’ house in England with an overnight stop at a hotel in the moors in Westmoorland.
So I have learned that it is good to have your stuff in more than one building. Currently backups to the internet are great, but they are slow. If multiple machines are backing up to the internet at the same time then that is not good, the crapfulness of Apple's backup protocol design are revealed.