Why you should borrow w bitcoin? For the same reason that you borrow fiat, you should take a loan if you have an idea for a productive activity but you dont have the bitcoin at hand.
like borrowing bitcoin inorder to invest to a coin which you know can skyrocket in a week.
and then payback with interest after you withdraw and profit. opportunities like these are suppose to be grab. If I only knew monero will go that high before a week ago, i might just sold the rest of my XAURUM and LTC to invest to it.