WHAT IS CNC?
With Computer numeric control you can stop proccess, change settings, continue and save it with last shape. So just installing control interface for once is enough.
Before CNC there was NC. NC is using every workbench for metal and other materials. These benches are;
All NC benches has different abilities and characteristic features. So you can't make a job with wrong bench.
NC benches doesnt have any memory. These kind benches reads blocks and does these blocks. After operations done machine goes other block. This proccess goes like that till the end of program.
Actually CNC and NC are kind of same machine but CNC has a lot of features than NC. So you can make some jobs with CNC even you can't with NC.
You can save programs in memory. There is a power supply for control unit. If energy of bench will go, memory will be still in there and will be saved. Changes for program can be done easily. This program can be saved. Some routine proccess are saved as cycles in program. If you want to use a program a few times you can write it as sub-program so you can bring it everyone when you want. You don't have to setup dimensional shifts because CNC benches can set everything up for you. There isn't any need to manuel things for changing cutters. Rotery turrets are using for this.