Also.. The catch here is how would a Dom/Domme figure out that it's time to go easy on the sub OR to push/force him to do as told? (Considering the sub has already conveyed to the dominant that he likes being forced).

The sub could be begging the dominant for mercy but it's something not serious/harmful enough for the safeword to be used. Though I like being pushed but also there are times that a sub could be let off the hook. If the dominant lets the sub decide stuff then it also hampers the whole power dynamic.
How do you people deal with this?

I can provide a scenario that could be my case : If I ever had to eat my own cum then I'd probably not be able do it.(atleast not by myself). But then there have been rare instances where this thought gave me a thrill.(I am into humiliation and degradation). Being in the subspace can be incredibly motivating. May be I'll actually do it if my Domme made me do it regardless of my excuses and begging and offering to take up any punishment instead.

I am trying to be as clear as possible. Not sure if it makes sense for everyone. If I confused you people then I can try rephrasing.