You may not want to accept something completely unrelated to the field that interests you most. You may want to make sure the company is stable. You don't want to get caught in a massive downsizing soon after you are hired. You want to find a place where you'll be comfortable. If the job calls for expensive business suits, the polo shirts you wore at your last job will need to be replaced immediately.
Some employers offer an advance to pay for such prejob expenses.
This money also could be used toward relocation.