Save fuel ?
Don't forget there are times when you will want to carry the bare minimum.
Like say forecast TX in the area. Delayed departure to coincide with busier arrival traffic at destination. Local knowledge of factors outside of flight planning contingencies.
This way, we could also add value to our customers' experience by adding extra stops to their trip. Thereby broadening their horizons. This could also be charged extra for, as in say an "extra landing" surcharge on the ticket.
The decision making process is packed with danger !!
FG