It is easier to pay for.
It is easier to resale the points in the future.
It can be easier to divide the points later between children, if you wish.
Look at when you want to go to DW and look at the points required for the stay and make sure 50 points are enough. Sometimes it is better to buy the odd number (i.e. 58 for a 2 day stay in a studio, MK view at Christmas) rather than just the 50.
You can finance a purchase over 50 points, or pay cash for a purchase over 25 points.