Freesync doesn't limit your FPS, freesync means if your FPS DID ever fall below 75fps, your monitor would lower it's refresh rate to compensate.
My 27" 1440p 144hz monitor for example has a freesync range of 48-144hz. So it can on the fly adjust itself between 48hz and 144hz to match my framerate.
if my framerate is constantly above 144fps, then it will stay at the maximum of 144hz on the monitor. However in games where my framerate drops below 144fps, my monitor will also drop, as far down as 48fps. This avoids screen tearing and stutter that you'd get otherwise with a constant 144hz refresh rate.