practical applications for synchronous and asynchronous communication

I want to find the practical applications for synchronous and
asynchronous communication. In what situations we use synchrnous and in
what situations we use asynchronous communication. I understand
synchronous communication means that the sender needs to wait for
repsonse from the receiver before sending another request. But
asynchronous communication no need to wait for response.

I got the basic concepts, but need to know the practical applications
and examples.

please advise. thanks!!