So what's the deal with spark plug washers?

MOPAR faithful: I know this has been discussed before, but could someone please explain to me why you're supposed to remove the washers from the spark plugs that you install in your slant six? I have a 74 Duster. The washers are there and the motor runs fine. I torque them to 30 foot pounds just like the service manual says. You cannot remove the washers from the NGK plugs that I use. What kind of washerless plugs do you use in your mid-1970s slant six?