My question is: why would you do satin on the walls?!

More info needed. If you wonder about difference just use flat on ceiling and walls. There will be a slight perceptual difference due to the different planes. Walls vertical plane and ceiling horizontal plane.

No satin on walls please. No sheen level higher than eggshell, unless you are talking about walls that are trimmed ( wainscoting ) .

Ceilings are best flat finish . .....and best a shade lighter than walls. Unless you mean tinted another color entirely, such as the faintest suggestion of "sky"..............

Satin paint is the brightest of all wall paints and can be easily wiped clean.

IMO matte finish is the best for walls and ceilings . There are washable matte finish paints. Any sheen on walls will reflect light badly and show every tiny little imperfection is the drywall job.

Lisa, Chantilly lace will look white. Do flat on the ceiling. Do not do satin on the walls; do Matte. It is a nice velvet finish and is washable. If you must have a bit more sheen no more than eggshell.

If wash-ability is important, an eggshell finish will do it.