As you may or may not know, clenched_hands also went through some purging process recently (luckily I know who did this time!).
Though there can be at times overlap between the two, overall I think they fit different types of postures and emotions.
clenched_hands specifically tends to have the hands pointing up, down or to the character itself rather than forward.
I could get behind a clenched_hands -> fist implication though, if other people want it.
We might want to clarify the definition of fist as well. I would tag it only when there's some dynamic posture or emphasis involved, but apparently others seem to use it about anywhere, notably on cat_pose.
e: horrible typo.
Updated by jxh2154