Of course you don't need to use a cable release. Just use the shutter button if you want.
Dan, The reason for wanting to use the cable release here is that the Medalist I locks out the body release when the accessory sheet film/ground glass back is used.
The Medalist I has an infinity lock on the body shutter release so that it can't be pressed when the camera is focused back past infinity.
It also has the ability to re-calibrate the focus scale and rangefinder when the accessory back is used to account for the film plane offset.
However, it does not re-calibrate the infinity lock when the accessory back is used, so with the focusing helical being further back, the body release is now locked out at around 4 feet and further. You can press the body release down to unlock the film advance, but it won't fire the shutter.
So, practically speaking, you have to use a cable release to fire the shutter while using the accessory back, then once the exposure is made press the body release to unlock the film transport and wind on.
I believe the Medalist II removed the infinity lock out to alleviate this issue, but don't quote me on that, as I don't have a II to compare.