As you can see, there are various approaches to running jobs and setting cuts. Ideally, machinists strive for the most aggressive cut they can get away without quickly ruining cutters or trashing setups. Often, the limiting factor in terms of aggressive cutting turns out to be the rigidity of the setup and the strength of the cutter. An additional factor to consider is that parts become weaker as they're machined.

Machinists have to be intuitive stress engineers. They constantly have to make judgments about the aggressiveness of cuts based on the type of material they're cutting, the rigidity of the machines, the rigidity of setups and the strength of cutting tools. It's a skill that comes with practice.

It is unlikely any two machinists would run a job the same way or at the same rate. Most machinists wouldn't run a job themselves the same way each time. There are simply too many variables and too many different ways of doing things.

Occasionally you'll hear a machinist say "Why should I work fast? I'm in no hurry. I get paid the same hourly rate regardless of how fast I work." That may be true, but by learning how to work fast you'll have that option when you need it.