My publicly facing servers get patched as soon as I'm aware there are updates available. If it borks anything, I just turn to the previous backup (not that this has ever actually happened).
They are appliances, and if they work they work. Unless something is broken, I leave them alone.
The only exception so far has been the robot lawn mower, that supposedly adapts to weather forecast. But it will be jailed soon, too.
If the manufacturer doesn't support the software anymore (or better yet, is out of business) the odds of malicious updates go way down.
1) Manufacture's suggested update schedule.
So don't buy printers, basically? That's sarcasm, but, non-sarcastically, do you know any printer companies that (make decent printers and) have basic respect for their users?
If you need to print in color, you can buy an inkjet printer that uses ink tanks instead of cartridges. However, you generally should be printing at least once per week as otherwise you'll need to waste a bunch of ink on head cleaning cycles. The other thing is that all inkjet printers (including ink tanks) clean their heads by spraying ink into a pad called the "waste ink reservoir". After a couple years of use, the pad will become saturated with ink and the printer will refuse to work. Most printers have the pad integrated into the printer, so you have to throw out the printer at this point. Look for a printer with a "maintenance box", which is really the waste ink pad in a user-replaceable plastic cartridge.
If Brother ever truly loses the plot, my next printer will be the local FedEx store. Life's too short to fight hostile hardware.
A recent (as in the past two years) update removed that benefit. Now it fully refuses to function in any capacity if a colour cartridge is out. It won't let me print fully-black content, and it won't even let me scan.
So Brother are no longer one of the good guys.
https://web.archive.org/web/20190805123707/http://www.seeing... https://en.wikipedia.org/wiki/Printer_tracking_dots
Today, Epson for inkjet and Brother for laser.
And never buy an HP Printer which should come before any talks of when to update.