I can get to my drain plugs & filters without jacking up the motorhome. If I'm just doing a routine oil & filter change, then I usually won't jack it up. If I want to perform a more complete inspection, then I'll jack it up to give me more maneuvering room. I don't bend so well anymore! LOL
As others have said, always put jack stands under the rig if you do raise it up. The hard part is finding jack stands that will support the weight of the rig.
IF I remove a tire (not an easy task on many class A's, the lug nuts on ours are torqued to 475 ft-lbs, and the tire/wheel probably weighs 150+ lbs.), I put the tire under the side of the chassis to give some added protection should a jack or stand fail. I do the same when working on my cars.
Be safe!
~Rick