In my case - DW thinks its leaning after putting out the slide... so a level doesn't matter..
Our larger slide is on the drivers side... I go just a touch past level on that side before deploying the slide - and she is happy.
Deploying the slide certainly alters the weight distribution... If the full load is on the jacks - it shouldn't make a difference - but if the suspension is in play at all - it certainly can shift.