If you don't have it your transmission won't drop down gears all the way when you stand on the gas. My truck currently doesn't have it hooked up, because my carb came off a manual trans car and doesn't have the bracket for it on the throttle shaft. If I'm cruising at say, 35 mph, and come up to a turn and take it at 20 mph my truck will stay in third gear. If I press the gas pedal down far enough after making my turn it will eventually drop into second. If I had my kickdown hooked up, it'd drop down to first if I stepped on the gas enough after making my turn at 20 mph and take off like a rocket. If I want it to drop down like that now I have to do it manually by moving the selector. It's not a big deal for me as I love the operation of my carb and don't really want to mess with it right now to get the kickdown functioning. If you're at a great enough speed (out of the range of first gear) it won't drop it down to first like in my scenario, it'll just go into second like it would without the kickdown attached.

If you DO go find a kickdown rod and hook it up to your Edelbrock carb, you'll need an adapter for it. Something like this.
I'm not sure if there are different rods for different auto trans. I'm sure someone else will be more knowledgeable on that subject.

 

D3TZ-7A187-C .. Kickdown Rod / Obsolete ~ No Ford dealer or obsolete parts vendor has any.

1973/76 F100 & 1975/76 F150 302/C4.

Shown as 7A187 in upper pic:

 

They are kind of universal on the models, specific when produced. You can check around salvage yards and come up with something close, put some bends in it yourself. Cut shorter and weld or lengthen. Try LTD's, Tbirds etc. around the same time frame. With the edelbrock carb stock kickdown needs a extension anyway sometimes.