There are quite a few shortcuts to repairing exterior wood. If anyone is using anything other than a two part woodfiller they are probably doing it on the cheap. However, although it is a good product the 2-pac (as it is known) is not really that brilliant a solution. It sets hard and doesn’t flex with the movement of the wood so you always seem to get cracks appearing and then after a couple of years the water starts getting in and rotting the wood.
The best solution is to use repaircare products. They dry like a fibreglass finish and stick permanently to the wood. They are an expensive solution (the stuff costs £35 a tube and you have to buy the adhesive with it which also costs a lot) but if it’s done properly you should get a solution that is guaranteed for 10 years.