Hi Colin
My ML7 has been sitting on a wooden bench not bolted to the floor for the last 30 years and is quite stable. My late father's lathe, a slightly heavier machine on a commercial sheet metal cabinet, was initially bolted to the floor and was an absolute pain when it had to be shifted. Subsequently it was left unbolted with no issues.
As an aside, my big lathe ( a bit under 2 tonne ) sits on six rubber loaded dampening feet, again not bolted to the floor and again quite stable. These feet ( not an inexpensive item ) are specially designed to reduce noise and vibration – good or me and good for the neighbors. Incidentally, the weight of this beast, distributed over its six feet works out to about 60 lbs per square inch – or about the same as me standing on tip toe on one foot. As the floor is a 125 mm thick reinforced concrete, I don't think there is a great risk of either the lathe or me sinking through!
I recommend the fitting of adjustable feet on any work bench, especially those feet with a rubber "sole" which helps iron out vibration. For smaller loads these are quite reasonably priced and, as Rob stated above, is helpful in leveling – both the bench and the lathe.
Pero