This is an old thread, but alas.
I enjoy jumping, but I think in some cases it is over done. It should only be done once a week at the maximum IMO, for many even less. Overjumping can wear on their minds and joints. The right amount of jumping should give them a good hind work out and sharpen their minds. I find it to be a great cure for horses that have been doing only dressage or EP for the past few months and are getting work sour. However, I do find poles and cavaletti more functional for my dressage work than a jump, as well as having a lower impact on their joints.