Answer
It is to keep your body in contact with a metal area of the computer
Explanation
ESD is the Electronic Static Discharge. This is the sudden flow of electricity between two electrically charged objects.It normally runs in dry environments ,socks, carpeted rooms and also when one is wearing friendly static clothing mostly clothes made of wool. So when you keep your body in contact with a metal area of the computer this will easily avoid ESD while working on your computer.
