When do you typically change spark plugs?

[Diggs24]

Sealant

 

[StorableComa]

I just changed mine at 40K Super easy DIY. Took a short drive to warm engine up....coils came right out.
Low RPMs seem a little smoother now.

One strange thing. When I finished I notice a red goop on my spark socket. It was really sticky... when I tried to wipe it off with shop rag...the rag got stuck. Had to use a degreaser to get it off.
Is some type of grease from the factory? Don't recall seeing this in any of the online videos I watched.

Anti-seize?