The Tornados did the same under spi with the alu mast, but then it was risky. It was easy to break a mast if you overdid it. With the carbon mast the risk of breaking the stick is much lower so everybody do it.

The idea is to realease some sheet in the gusts when you become overpowered. The Alternative is to release the traveller somewhat or turn downwind. The traveller is a very coarse trim adjustment and turning downwind is even worse. With the mainsheet you have very fine control and it is fast. Letting the sheet out a bit in the gust and then sheeting in again to a nice trim is fast.