It is never useful to borrow money or bitcoins as you have to give back more
There are very specific circumstances in which borrowing is useful and that is if you want to engage in a productive activity but you dont have the cash in hand, in this day and age people borrow money just for the Lulz, but in the past this was the only valid reason to borrow.
Well you are right with it, it is going to be useful to borrow if you are going to use it for your profitable activity. And you just need to make sure that you are going to make it real and get good some profits out of it. Because if you are not going to get good profit out of it then you are just going to work to pay your borrowed bitcoin with interest.
At bitcoin lending i doubt the profitable activity is a need, we do lend our bitcoins to get some interest, something i consider less risked then invest into some altcoin, has i made in the past and lost several coins. Soo lending is something that may bring you profit, as long you work with colateral, otherwise you may be donating bitcoins instead lending.