As you can see, level is a state of mind... some are particular, some not so much. Drives me nuts if not level, but that's just the way I roll.
Beyond that, the two most important components affected by level are slide rooms and absorption refrigerators. The fridge has fair tolerance, but I don't move the slide until I'm nearly perfectly level. Knock on wood, but my Schwintek has behaved itself so far... I like to think being level is a big contributor.
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