best practice for unused ports

Hi all,

What is the disadvantage or risk about leaving some unused ports and aggregrate ethernet ports are open and not disabled.

In the CCNA course, trainer always strongly advised on shutdown the unused ports. How about in Junos EX switches product?

1-)Any traffic goes to unused ports unles plugging any cable to unused ports?

2-)Does EX switch has any machanisim to avoid unusual behaviour when unused port or ae are left open....

3-)what is the best practise for unused ports and ae(x)?

4-) If persisting in keeping open unused ports, what is worst scenerio?

Thanks

Ar