must i use home sharng for apple t.v.

You should use Home Sharing to share your iTunes content, Airplay to mirror your Mac.

you don't have to

home sharing is letting your appletv access what is in the computer shared itunes lib

airplay mean the appletv is used as remote speakers for a computer or for an ios device

airplay mirror mean the apptv is used as remote display / speakers for a newer mac or a newer ios device