If your table run a little faster or slower, a speed controller can correct it, another benefit is you don't need to move the belt/pulley for 33.3 to 45, just push a button like a DD table.
a guy from stevehoffman forum use a Project speed box with Marantz TT-15 :
http://forums.stevehoffman.tv/threads/turntable-speed-controller-do-you-use-one.562398/page-3
But the Marantz motor is 5Watts and the Project box is rated up to 3Watts, not sure it actually work
a guy from stevehoffman forum use a Project speed box with Marantz TT-15 :
http://forums.stevehoffman.tv/threads/turntable-speed-controller-do-you-use-one.562398/page-3
But the Marantz motor is 5Watts and the Project box is rated up to 3Watts, not sure it actually work