In reading these forums for many years I have read that some RV's. the maker feels, it would appear, that the battery they installed is not enough to move the slides without help so they insist the engine be running (Alternator power) Another theory at end of post.
Others feel it's not safe to drive with the slides moving about so they insist the motor be off (Of course they put in enough battery) Mine is this way. However the JACKS are another story.. They need ignition on. on my rig.
Theory 2: Hydraulic slides, Engine powered pump (Power steering more than likely) this one actually makes sense.
Home is where I park it!