FHA does not require that collections be paid, but many other loan programs will require them to be PIF.
If you get a good LO and a great mortgage package but the lender wants the collections paid then that is probably worth it. If the place seems shady and the LO starts telling you to pay stuff off prior to close then you might want to check around.
Even within an FHA loan, each lender and/or investor can have their own qualifications for what they will or will not accept. Alot of people want collections paid off to make sure you don't get into any lawsuits or such. Also, refusing to pay a collection that is valid looks bad to a lender or investor as you are not meeting obligations.
It is definitely a case by case situation.