The best shops use simulation tools, but you need the 3D models / configurations of everything to make them work, and then the machinist still needs to load everything correctly. It's very easy to make a mistake.

Check out a simulator here: https://www.ncsimul.com/

There's a lot that can go wrong, and it's too much work & tech integration for most shops to make the investment.

Even if you have the 3D models for everything involved: tooling, tool holders, stock material, fixtures, CNC machine, along with the instructions for the movement of all of it, there are still many opportunities for both configuration errors and runtime crashes.

For instance, CAM tools usually simulation axis movements only, before they've been converted to gcode/NC. If there's a bug in your post-processor that generates gcode or if it doesn't perfectly match your machine configuration, you're going to crash.

Even if you use a simulation tool like Vericut or NCSIMUL, which both simulate using the actual gcode, the physical machine settings may be out of sync, or there could be a wrong piece of stock material loaded or some foreign object (a wrench) that causes a crash.

Probing routines and careful selection of Work Coordinate Systems can help verify/eliminate some of these unknowns at runtime, but it's still no guarantee that the part will come out right.

Hardware is hard!

Most decent CAM software has at least some simulation routines, which is helpful, but definitely not definitive. There can often be errors such as defaults that are bad in some situation that create a lead-in/out that tries to clear the tool, but actually digs the full length of it into the solid material, and this might not be noticed in the simulation.

I've also frequently mocked up styrofoam stock material and run the entire toolpath through that, which can be very helpful, but again, not definitive.

Ultimately, you need to just be really careful about the toolpath creation, and watch the first run like a hawk, which can take hours. Pausing and starting each new segment at a fraction of normal speed can help also.

The cool thing is that once you've run the toolpath a few times and can trust it, you can almost start it and ignore it while the part gets made (note that the operative word is almost).

Even with the difficulties, when you have a good machine and some skills (and patience), it is quite rewarding what you can make!

Some CNC machines, like the Bantam Tools "Othermill", have software that does a "test" and will tell you if you'll crash into the board, and can recommend drill bit sizes. I'd highly recommend this machine btw, excellent support and I've been very happy with the results for both wood and PCBs.

You can put all your workholding devices (vice, clamps, etc.) and toolholder into your CAM software and it will find some crashes during simulations.

Most CAM will do good simulations.

I usually run a new program without an actual cutter in the spindle. Then I run it with the cutter but 2-3" above the actual material to be cut.

Many people will do trial runs on machinable wax.