This method gives you a two fold benefit, 

 - When you so choose, you operate at the peak human condition. Not superhuman (as that would shatter your bones, ligaments, muscles ...) but peak human. This is very important for adventurers, soldiers, crime fighters, fire fighters ...
 - (The more advantageous one) You can maintain this peak condition for the duration independent of your physical state.

If you can channel this virtual muscle mass, you are also able to avoid the drawbacks of exhaustion, by gradually exhausting the virtual muscles at no expense to your physical body. 

Model situation: Cattle is being raised for the purposes of "powering up fire fighters", each firefighter is at all time being "charged" to allow operating at a peak human condition for at least 48 hours without a need for rest.
During normal operation (a fire occurs) they arrive at the scene and can channel this virtual muscle to break down doors, carry victims .... 
In case of natural disaster, they will be able to operate at the site removing rubble, transporting, people and material at peak human condition for tens of hours straight, thus being a tremendous benefit.

Same for policemen, soldier, mountain rescue ...

Another application that came to mind a messenger per this article: https://journals.physiology.org/doi/full/10.1152/japplphysiol.00947.2009

Run speed of 69 kmph is physically possible. Imagine you can  maintain this speed for 24 hours. In under a day this messenger can run from Paris to Rome.