The STD allows you to use long microphone cables or microphone tie lines to extend your guitar or any instrument cable without the loss of tone and increase of noise associated with long instrument cable runs.
It also has two outputs for splitting between two amps or between an amp and a direct injection box, with a selectable ground lift on one output to eliminate ground loop problems.
The STD is a perfect solution for: the live player who is tired of the tone sucking wireless rigs but still needs to be able to walk more than ten feet from his amp; the studio player who needs his amplifier in isolation, but himself in close proximity to his band mates; the recording engineer using control room rack mounted direct injection boxes with a player located in the studio or isolation booth.