If you read the instructions, on mine anyway, it says a full load is to the top of the basket without pressing down on any of the clothes. I always lay them around in a circular pattern to even out the level of clothes as I'm loading it. My fiancee used to shove as much as she could in there, and it would get off balance and wobble and shake the house. It took a lot of convincing but she finally believed me after I kept pointing out that's probably why it was happening.

Washing machines (mine anyway) wash by spinning back and forth in water with detergent, so if you stuff it full there's not much room for any clothes to move and they don't get very clean and will come out smelling like laundry detergent.