People spend weeks on color and thirty seconds on sheen, then wonder why the finished room does not look like the sample board. Sheen controls how much light bounces off the surface, and that single property determines how washable the wall is, how much of the wall's texture and repair history you can see, and how deep the color reads.
The rule that covers most of it: the flatter the sheen, the better it hides, and the worse it cleans. Flat paint scatters light, so patched drywall, roller texture, and the gentle waviness of old plaster all disappear. It also marks if you scrub it. Glossier paint reflects light in a straight line, so it wipes clean easily but shows every dent, seam, and sanding mark you left behind.
For ceilings, use flat, always. A ceiling is a large uninterrupted plane lit from below at a shallow angle, which is the cruelest possible lighting for a surface. Any sheen at all will reveal every roller lap and every taped joint. Nobody scrubs a ceiling, so you give up nothing.
For most walls, eggshell is the right default. It has just enough sheen to survive a wipe with a damp cloth but still hides ordinary wall imperfections. Step up to satin in bathrooms, kitchens, mudrooms, and hallways with small children, where moisture and hands make cleanability worth the extra light reflection. Reserve semi-gloss for trim, doors, and cabinets, where you want a hard, wipeable film and where the crisp light reflection actually looks intentional.
One Minnesota-specific note: in the dark half of the year, our indoor light comes mostly from lamps at low angles, which behaves like ceiling light and exaggerates sheen. A satin wall that looked reasonable in July can read glossy and blotchy in December. When in doubt in a north-facing room, go one step flatter than you think you need.