It's called MP washing. I only have a vague understanding of how it works, but i'll try to explain it as best as I can.
When you level with ints, you add your points into MP instead of HP while you're wearing int gears. Then you take those points out of MP and add into HP. You'll lose those AP for now until you level more and gain more MP. Basically, it helps raise your MP higher as if you were wearing int gears longer (for those who didn't wear ints at lower levels).
only seriously rich people or people who waited a long time to wash (old characters) should do this. Otherwise just normal wash and don't forget ints.
When you level with ints, you add your points into MP instead of HP while you're wearing int gears. Then you take those points out of MP and add into HP. You'll lose those AP for now until you level more and gain more MP. Basically, it helps raise your MP higher as if you were wearing int gears longer (for those who didn't wear ints at lower levels).
only seriously rich people or people who waited a long time to wash (old characters) should do this. Otherwise just normal wash and don't forget ints.