Hey i am building a router tabel (size 28" x 72") with belt drives. The belts will be fixed on both ends.

Some step motor driver have an automatic feature to lower motor current anytime the motor is left at rest. Lower motor current=reduced holding torque. Does this mean that the axis can slip away due to the "low friction belt drive" while other axis's are working?

I think this feature is designed more for screw thread based motion, where the thread teeth will hold the axis in the right position with little to no power to the stepper motor.

I believe your concept of what would happen if you implement this "feature" on a true belt drive arrangement is more or less correct. At the same time, it normally takes a lot less force to "hold" a position than to "accelerate - reach - decellerate" an object, so this often will still work fine for you.

One reason this concept is used is that stepper motors will get hot from use. Some people like "chopper current" based systems, which are sort of a pulsing action to the stepper, and others like a more linear driver based approach (like a linistepper driver ) Both concepts work, but there are some differences (such as the motor inductance) which sort of force a "decision" to one path or the other.