We are very goal orientated in the health professions at times. That's not a bad thing, but as resources get squeezed, and workloads go up, the pressure to achieve outputs and throughputs increase. Time becomes a precious resource and wasting it becomes a crime.
Mary had a precious resource - nard. Nard is an aromatic oil, believed to have medicinal properties, and highly valued for its strong and distinctive perfume that clings to skin and fabric. It was incredibly expensive, so only a small drop was ever used (or needed). This jar may have been an inheritance - all Mary had that was of value, so using it like this was extraordinarily extravagant. No wonder Judas was outraged. 
Mary may have had a foreshadowing of Jesus's imminent arrest and execution, but she certainly knew that in the view of her peers, 'wasting' this much perfume on one man's feet was hardly a good use of her precious resource. But to Jesus, this was the most loving, precious gift any of his disciples had given him. 
When we offer time to people, it is a precious gift. Especially when we give it to those not esteemed in our society. Time spent with the dying, the very young, those with disabilities, the foreigner and the homeless. That extra time at the end of a shift or appointment schedule to listen to a patient who just needs to offload; going out of your way to talk to that awkward or demanding person at church or in your street; giving your time to stand up for and campaign for those the world does not esteem. These bless not only those people but are an offering of worship to the Lord himself. 
Others (especially colleagues and managers!) may see us wasting time. Others still will feel uncomfortable that we are focusing energy on people that they would rather were not in the public eye. But as Sheila Cassidy put it 'there will always be those who find themselves called like Mary of Bethany to disturb the peace by pouring out over some dead loss to society that which could have been sold for three hundred denarii.'