I've noticed that some planes cage their attitude indicators when Parked and uncaged them after start. As seen in this Lear 35 checklist. Why is this?
The standby attitude indicator on the Lear 35 has its own power switch; it's not automatically energized when the battery masters come on. Therefore it doesn't spin up on its own when power is applied to the rest of the aircraft.
If it's uncaged before it spins up, it could be damaged, and unlike the other gyros, it doesn't begin the spin up process until you flip the switch. So you power it on and leave it caged until it's up to speed, then you uncage it. Similarly during shutdown, you cage it first and then remove power so that it can spin down safely.
A - Standby attitude indicator
B - Caging knob
C - Power switch
Original image by Don Popp, found here. Image is in the public domain.