everything in math has it s uses .
for example zero has many uses,it is used to represent nothingness.if there was not zero ,we would have used terms like 1-1 for representing nothing.
negative is used exams to make the competition tighter,without negative symbol we would have never been able to subtract!!!
positive numbers are used in so many places like it is used i valuing money,scores in games etc.
i hope this helps u...