To add to what Michael has posted, you can transfer points only once per Use Year, either into or out of your account. It can be difficult to find someone willing to use their one transfer to transfer only 10 points. Also, the One-Time-Use points can only be purchased when making a reservation 7 months or less from check-in because those points have no home resort priority.
If I am short a few points when making a reservation in the home resort booking window I usually borrow points from my next Use Year. When short of points when booking 7 months or less from check-in, I might borrow points from my next UY or I might opt to purchase OTU points if I'm saving my home resort points for another reservation that I want to book 11 months out.