It is not compulsory to use shoe trees, but if you want to preserve for a long time the models you love it is definitely worth it to have some adapted to your model.
The shoe tree enables the shoe not to be deformed or to get misshapen when it is not worn. It also prevents the leather to take a bad shape - and existing walking folds to settle permanently and grow.
It maintains the shoe open and thus permit it to be properly ventilated. Furthermore, the Melvin & Hamilton shoe trees, being made of cedar wood, diffuse a pleasant scent.
With decreasing prices, the more you buy at once, the lower is the unit price!