I have my GPS receiver (Trimble 332) wired hot with a toggle switch so that I can leave it on overnight to maintain convergence during planting season.  The other devices are powered separately and shut off at night.

I actually have the 332 wired to a small lawn tractor battery.  The small battery is connected via a diode to the main system on the tractor.  The main battery charges the small battery.  The purpose of the diode is so the load of starting the engine will not cause the voltage to the 332 to drop.  Without the small battery, starting the engine on the 8120 would sometimes cause the 332 to drop out.  This defeated the whole idea of wiring it hot to maintain convergence.

If the 332 were left On for long periods of time, it might draw down the small battery which could eventually draw down the large batteries.  I have not had a problem in this regard.

On another tractor, I have a CFX-750 running Autopilot.  This is the tillage tractor.  It is wired hot but doesn't have the lawn tractor battery involved.  My retired brother drives this tractor and we have him just leave it On during the planting season.  This is only on WAAS so the convergence isn't an issue but it is just easier to leave it on for  him.  We have not had it draw down the battery on this tractor either.