Because we all have junk we shouldn't park on top of a router
Just in case you ever want to NOT sit right near/under/over the strongest wifi in the building and end up feeling like a Nora Volkow test subject.
Wifi "bar" indicators 
do a great job of indicating the relative signal strength of the network you are currently connected to.
What about all the other networks near you? If you don't mind inadvertently sitting on top of an industrial strength router it's your prerogative.
If not, you may find Hotseat useful.
The average wifi indicator only reports the signal strength of the network you are currently connected to.
If there is a spiffy new Industrio-megapower-wifi-5000 unit in that cheap drop ceiling right 4 feet from your head it'd be kinda nice to know.
The OSX dmg installer is here
This project is licensed under the MIT License.