It isn't the only reason but, yes a dollar is a dollar. I guess when you spend the big bucks on a vacation you don't worry about such things but I am on a limited budget.
The main reason is that if he exchanges the entire $1000 US and then something happens (i.e. an accident etc.) that doesn't allow him to spend all that Jamaican then he will lose again when he has to sell it back.
He asked for my opinion and I gave him mine. You should do the same instead of criticizing another person's opinion, don't you think?
Peace and Guidance