Modern RV's have hydraulic/electric 'feet' that extend down and both stablise and level out the rig. These take time to put up and down and are very obvious when the are extended. If you just park on a couple of bits of wood, it's possible to get it level enough for the fridge to work OK. It doesn't look as obviously 'parked' to the casual passerby. And if you need to make a speedy getaway (for whatever reason, be it the law or unwanted company) you can just start up and drive off. That's what the wood is for.
They've also gotten a bit better at surviving sloped operation; modern ones can be operated while driving and for short periods parked on a slope. Older ones were more sensitive.
Also, sleeping on a tilt is uncomfortable. So, leveling is kind of useful for humans (and dogs), too.
Reminds me of the joke about the engineer: "hey, why can't those blind guys just play at night?".
;-)
Also, how living on a RV impacts "Don't drink and drive" ? :)