integra_blurred,
I use anti-seize in a whole bunch of locations. Most of the time it is where there is the potential for high heat (as in spark plugs and O2 sensors, manifold bolts), high corrosion potential (bumper bolts, or any other external fasteners) or where there is dissimilar metal (such as alloy rims on cast iron disks or drums).
It's not a big deal if you don't put it on the spark plugs as you shouldn't torque down on them too much. But if you want, you can certainly pull them and put a dab on the threads.
There are also a number of types out there, either the silver molybdenum based stuff or the orange copper based stuff. Both are pretty nasty to deal with, but bothwork just fine.
Bogatyr