Once you have your ShapeOKO built, it's time to tune it for optimal performance.
Belt tension is a balance. The belts should be as loose as possible while still eliminating backlash effectively. If the belts are too tight they put unneeded stress on the machine. To tighten the belts, pull them just taught and tighten the clamps. Rotate the pulley one step, and see if the carriage moves. If it does, rotate it one step in the other direction. If the carriage moves again, then the belts are tight enough. If not, then tighen them a bit more and try again.