The short answer is, use locktite on something that you feel needs to be secured from loosening, and use anti-seize on somthing that you feel you may have a hard time removing later, such as sparkplugs, especially in aluminum heads.

I usually like to use locktite on things that rotate, like bolts on a flywheel, etc.

I'm sure some of the expert engine builders on here will have other uses and opinions, but I think this is a general rule of thumb.

The most used locktite is the "blue", although there are stronger versions like "stud and bearing mount" that are very difficult to get loose, and are used on things you don't want to ever come loose. Blue is removable when used.

Hope this helps a little.

Don