To close the loop or not

I'm doing a CNC conversion of an RF-45 clone mill and have searched information about CNC controllers. I recently learned that LinuxCNC supports linear encoder feedback.

My machine will have ballscrews with double ballnuts and either closed loop steppers or servos. Now I'm wondering whether it will be worth the extra cost and tinkering to implement linear encoders for actual position feedback.

What kind of results can be achieved with linear encoders or without them? I want the machine to be able to machine as accurate parts as possible. On the other hand the machine is not industrial quality so it would be waste of money to build the control system more accurate than the actual mechanics are.

Any thoughts?

I have a FM4 called mill that looks quite similar, only guessed 20 years older. I run Nema34 plus changed x and y to ballscrews. Nice mesa 7i76e based electronics.
But nevertheless, she is not stiff enough that i would concider glass scales.
Mike

Is stiffness that important here? Spring passes are light and won't cause much flex anyways.

I think the main advantage with closed loop control would be ability to use cheaper ball screws as backlash and non-linearity could be compensated.