I’ll go first. After your turn the water off in the shower but before you get out, use your hands to wipe off any standing water on your body. Maybe even give your legs a bit of a shake. This way, you won’t drip nearly as much when you get out, keeping the floor and your towel drier.
I know that sleeping on your left side is best for heartburn due to the way our stomachs are oriented.
Not sure about other reasons. I like side sleeping with a pillow between my legs for my shitty back pain, but maybe that’s just me.