Isn't it quite obvious though ? Anyway I will break it down for you.
As per your example . you have 1 BTC, and you need fast lets say 4000 $ worth of ETH for 2 months . You know that possibly in 2 months your 1 BTC will be worth more , and you don't want to sell it today , thus the reason why people prefer to take a loan with collateral instead of selling it.
This is a good answer and I see it is right but even though I can do this sell it and making some money and then buy it again. But you know maybe the price won't go maybe go down.
your answer convince me but my opinion is sell it make some money and then buy it again this is better than get a loan while you have money
Thanks