For lightweight 'planing hull' boats - Easing off the vang allows the mains'l to grossly "power up" when you try to come come across the wind to 'feather up' ... as sometimes such gusts will have components of backing/veering/backing. etc. wind.... my technique (in lightweight 'planing' boats) is to keep the main a FLAT AS POSSIBLE and 'blade-out' when necessary rather than 'feathering up' ..... to keep the board/keel going in a 'straight line' as much as possible.
If in a lightweight boat and when on a plane, if the boat starts to turn too fast you risk 'tripping over' the board/keel (going somewhat 'sideways') and that can cause a 'dumper'. Lessening the depth of the board/keel allows the boat to skid rather than broaching or 'tripping over the board/keel'.