What is the difference between mh_arkit_mapping_anim and mh_arkit_mapping_anim_Preview?

Up to now, I know that when we use the metahuman character, what works in the background is “mh_arkit_mapping_anim”.

I also notice that they differ in “Animation->Animation Track Names”, but I don’t know why.

Can anyone explain in detail what the difference between mh_arkit_mapping_anim and mh_arkit_mapping_anim_Preview is essentially?

Thank you!!!