I borrow every year, but not because I don't have enough annual points. I habitually use all of my points before the end of the time when I can bank 100% of my points. I never want to be in a situation where I lose points because I didn't bank in time-- things come up, after all, and sometimes we just can't help a last minute cancellation. So, that being the case, I use all of my points about halfway through my use year. If I need to vacation during the last half of my use year, I borrow from the next year. I use the same number of points each year, just in a modified version of my use year instead of the actual use year.
It's a strange system, but it works for me!
HA! I just read back over my post and realized that I actually said that I had enough points!! This is NOT the case!! In fact, I don't really think that's possible.