I had a single license installed on 2 machines, which allowed me to use the s/w on one machine at the time. All of my machines are on my home WiFi network and if I already had any MS Office application running on one machine and then I tried to open it on another machine, I would get a prompt (forgot the exact text) that in essence told me that the s/w was already running on another machine. All it took was for me to go to the other machine, look at the dock to see which app was running there (Word, Excel, MS, or Entourage) and quit it (Command-Q works fine). Then I would be able to open any MS Office app on the other machine. So yes, you would most likely be just fine with only one license on 3 machines, given that you only use 1 at a time.