Not entirely true, an encoder can improve the stiffness of a step motor control system and
has measurable benefits especially if a step motor is combined with a linear encoder.

I think I need that explained to me in simple words. Are you suggesting that you need the linear encoder to deal with elasticity (or backlash or slop) in the axis drive? I could understand that, with the proviso that I would never build a system like that.

Cheers
Roger