This was my concern: Say I have a trip that requires 75 points. If I have a 100 point contract I can book the whole trip with current UY points. If I need to cancel, I have the option of booking another trip within the UY, but can also bank the points and use them in the next UY (giving you more flexibility). This can also come in handy for Fall Frenzy when you need to book close to 11 months out. You might want to reserve a room and decide later if you will actually take the trip... less complicated if you don't have to borrow points.
If I have a 50 point contract, I would need to book the trip with 50 pts from the current UY and borrow 25 pts from the next UY. If I cancel, now those 25 pts are stuck in the current UY. This is fine if you can rebook the trip within the current UY (and the room you want is available).
So it's all fine, but there's definitely more flexibility with a larger contract.