Two success stories:

In an office:

I had a client with a ~3000sqft office space, including a class room and a lecture room. They had wireless in the middle, but it wasn't strong and it couldn't handle all the traffic from their students. I ran ethernet through their drop ceiling, and mounted a Unifi AP directly into ceiling tiles at either end of the space. Their entire office now has completely solid WiFi coverage. Pretty much 4/5 bars no matter where you stand.

In the home:

Sadly, very few homes have drop ceilings I don't have the proper licensing to drill holes in people's walls, and even if I did, most of my home clients wouldn't want to spend the amount of money it would take to run ethernet to the other side of their house so I can install a second AP.

In a recent home situation, I decided to try something a little different. Instead of hundreds of dollars running cable, I charged them about $110 in parts (plus a little labor) to install MoCa adapters at either end of their house. I set up one Unifi AP at the router, and connected the other to the MoCa adapter at the other end of their home. It works perfectly, just as if it were a wired connection.