We should be careful not to define things only by their usefulness or perceived worth. That certainly wasn’t Jesus’s method. He refused to be ruled by urgency, and realigns the apostles’ zeal for selling everything to give money to the poor. (Remember the story of the rich young man? Selling everything all the time isn’t a universal rule for following Jesus.) In the case of the woman with the jar of perfume, it was indeed a waste on the surface. The entire bottle of perfume wasn’t even needed when it was being used normally, and to break the seal and pour it all out was an extravagant offering. Jesus recognized this, and saw that what appeared to be waste was an uncommon expression of worship.