When I did my wires I didnt put this **** on. I accidentally threw it out. How critical is it to have this, and where do you put it?

I don't think it'* critical. But you might have a helluva time trying to remove the rubber booties from the spark plugs the next time you try and change them. You can go down to your local auto supply place and get some (now I'm not sure of the exact name) either silicone grease or di-electric grease and lightly coat the inside of the booties with that stuff.

I think it helps to keep corrosion out.

It gives more contact area for the spark to travel thru too. Just go to a store, pick some up and slap it on.