There is no "one size fits all" for wifi/radio deployments, and radio itself is magic to most of the population.
Sometimes a single AP is fine for coverage (Centrally located in the coverage area, quiet channel(s), no single high-throughput device, construction that's conducive to passing RF).
Sometimes you need a bunch of APs (Lots of other users on the channel/high noise floor, buildings that block RF (tin siding, lath/plaster, wire mesh), or there's a device that's sucking all the airtime (""smart"" tv) from the other users on the AP).
Repeaters, mesh, powerline, etc are all hacks aimed at consumers. Professionals don't use that stuff. Pull a cable, it's not hard to do.
If one's working for you? Don't bother making it more complicated.
My old condo? with everyone blasting wifi all the time, and the jobless losers streaming tv all day? yeah, I needed 2 to cover that 740sqft+garage area.
Wiring the heavy-use devices will improve wifi as well. Get your TV's, media servers, and network-heavy workstations on a wired connection and free up the airtime for devices that need to be portable.