CFI experience is good for entry-level civilian pilots because most are young...it gives them an opportunity to get a little PIC in a commercial environment where you have competing priorities and pressures. You learn a little about responsibility, leadership, and complacency...

1000 hours of CFI is enough time to get complacent (around 400 hours), and then have the poop scared out of you later...which puts complacency in perspective. Civilians who have never worked in a high-risk business (military, LE, diving, fire-fighting, etc) will almost invariably become complacent in the cockpit if nothing exciting happens to them.

The cockpit feels like the inside of their car...but operating an airplane is really more like riding a motorcycle in traffic. If you hit something or lose control, you're screwed.

Older career-changers usually don't suffer if they skip CFI.