Discard()

[NedaABD]

Hello, I hope you are doing well. I wonder to know the exact function of discard() in example 2-4.

In the cheatsheet it is written:
qc.discard()
Removes a specified qubit from the QPU. Can be used as a method on the qc object or a QInt object. If called without an argument then discards all qubits associated with the parent object.

my question is why do we remove all qubits we just allocated?