Consider these two sentences:
“Let’s eat Grandma!”
“Let’s eat, Grandma!”
One little comma makes a world of difference (unless of course you’re a grandma-hating cannibal).
Or here’s another one:
“The team’s franchise quarterback resigned.”
“The team’s franchise quarterback re-signed.”
One properly placed hyphen can thwart a heart attack (unless you hated him and thought he should go anyway).