That kind of depends upon what the change is, and personal judgement. If it’s prob 30 of blowing snow, 50 knot winds and 400 metres vis I’d probably assume it was going to happen and take extra fuel. However, if the forecast was blowing snow, 50 knot winds and 400 metres RVR with a prob 30 of 10 kts CAVOK I’d probably assume it wasn’t going to happen and still take the extra fuel.
The big difference is that if I’m going flying for fun a light aircraft then if I decide not to drive to the airfield and the weather turns out nice, or the other way around it doesn’t really matter, there’s always another day. In a commercial operation if the forecast is above landing minimas and the wind below the aircraft limits then we’re going, the TAF helps us to reduce the amount of stress that we encounter during the day...