Patrick Hubbard of SolarWinds has written an article called “Wi-Fi heat map: Secret weapon for wireless network admins”.
It is an interesting read and I agree with most of the article. I will present one warning: heat maps are only as good as the information that has been fed to them. When loading maps into WNMS systems it is critical to calibrate the floor plan accurately otherwise your coverage will be over or under represented. Some systems allow you to select polarization of antennas this orientation is also critical for keeping the prediction somewhat accurate. If you do not add attenuation values for objects like walls, doors, and windows then the heat map is just a general estimation. Adding attenuation will make the prediction more realistic.
So as valuable as it is to see the estimation of your RF coverage, remember it is not a panacea and only as good as the info it has been fed.