Wall hooks make the most sense in houses with a real bottleneck at the door, mudrooms, back entries, narrow apartment hallways where coats pile up on the one chair by the radiator. If you already have a closet that fits everyone's coats with room to spare, you probably don't need them so much as want them, which is fine too.
The honest limit is weight and plaster. A hook looks sturdy right up until someone hangs a wet winter coat, a backpack, and a dog leash on it at the same time, and then it's hanging at an angle and pulling the screw out of drywall that was never meant to hold that much. Anything heavier than a light jacket wants a stud or a proper anchor, not just the hopeful little plastic plug that came in the bag. I learned this the hard way with a row of hooks that held for about six weeks before one came down, Carhartt and all, onto the dog's water bowl. Where they really fall apart is in spaces that get damp and never fully dry, a shed, a porch with no storm door, a bathroom with no fan, because the hardware underneath will rust or the backing board will swell before the hook itself gives out.
As for where not to put them, skip anything near a doorway's swing path, you will hit your head on a coat hook exactly once before you move it, and skip clustering too many at the same height in a small hallway, it starts to look like a coat rack had an argument with a pegboard. Wall hooks also don't do much for a room that already has a lot going on, busy wallpaper, a gallery wall, trim with detail in it, the hook just gets lost or fights the eye in a way that feels unfinished rather than deliberate. For color and finish, the easiest ones to live with are the plainest: matte black, brushed brass gone slightly soft rather than mirror bright, or a painted wood tone that matches your trim so it reads as part of the house rather than an addition to it. Bright chrome shows every fingerprint and water spot, and glossy white scuffs the first winter someone leans a wet umbrella against it.
Given a few years and some real use, the metal ones mellow, the brass dulls down to something warmer, the black goes a little matte at the edges where hands and coats rub against it daily, and the wall around them earns a faint halo from coats brushing past on the way out the door, which is its own kind of proof the thing was worth putting up.