Over lunch today we discussed TT (aka bootcamp). Why the mental and physical extreme was the question posed to me. I think there are two reasons. The first is to prepare the students for that day when they have to tap their deepest reserves (as students or as teachers). The second reason is simply the same as army boot camp. Break you down so that you just "let it go" and soak it all up. Us humans tend to over-think. Ee let our stupid brains get in the way too often. How much better do things typically go when we set aside our expectations.
I also spoke to another yogini at the Ann Arbor studio who would like to go to spring TT. Her masters' classes end in April (typical spring session starts b4 her classes end, so the late start this year is a boon). The money is of course a huge consideration (as it is for everyone). Job, savings, mortgage, etc concerns. I'm the oldest fart I know planning on going :)