Usually were not a fan of weighted planks but there are some clear benefits. It can teach proper bracing as it relates to weightlifting and gymnastics movements. Ensure hips are neutral and midline is braced in the same positions you would like to see reinforced. Keep the time under tension similar to the amount of time you would expect you be in the position you are trying to improve. Remember this is an assistance exercise so there must be a clear intention of the WHY behind this exercise.