Shutting off or lowering water temp

I have a boiler with an indirect. Even if we're away over night I turn it off and the water.
The only issue may be if it's an old boiler that's never been 'cold' it may leak.
During the heating season I'd recommend to only lower the thermostat(s) (not too low). The indirect may only call the boiler to fire once or twice for 10 minutes over the course of a day. If you have a mixing valve on your indirect, you could consider turning down the indirect's aquastat, then turning it back up when you get home. You'll have to make your own decisions about Legionnaires.
Generally when we get home from a vacation, I turn everything back on and we usually do a load or two laundry first, so I figure the indirect is back up to temp & hot water has gone thru the pipes. I also leave my boiler feed off and have a lwco.

I turn my system off for safety as I don't want to risk a disaster with water. I also never take a vacation when it's cold enough to need heat.
I don't really expect to see much of a savings lower water temperatures for a day or two. Insulate pipes, insulate building envelope for biggest savings.