(I don't know what has come over me - my mind is only producing grisly descriptions)
These will easily take a hand off so most of the machines designed after the mid-80s required the operator to press two buttons as a safety to cut and a pedal to initiate the clamp. The older ones from the 70s just required a push on a pair of foot pedals, or a pedal and a single button -- which was obviously stupid. Once the safer machines came around we got those.
I used to operate one as a kid in middle/high school before I went off to college. You can fit measure to sub-mm precision before clamping and making the cut. It was a really beautiful thing to see it cleave the edges off of several inches of paper like a hot knife cutting through room temperature butter. A real shame filling up bins and bins and bins of cuttings to toss in the trash (this was before recycling was a common thing).
Changing the blades was quite the ordeal and you had to do it frequency to send off for regrinding. At least on the machines we had. They're basically 20+lb razer blades.
Source: I grew up in a family printing business and we had machines like this to cut the margins and printer marks off of the edges of fresh printed material to help get it ready for binding or delivery. Almost every printed page goes through something like this.