Performance impact during the multiple callback functions after sending response

Can anyone explain , how the NodeJS works in the scenario like below

A request received and a function called but the response no need to wait for the function to complete, So I send the response back after next line of the function called. In this case, if another request is received, will the NodeJS wait for the function execution completion to take another request or it will take without waiting for the function to complete. How the performance impact occur in this scenario.

via Soorya Prakash