
I'm really trying to ask how many students benefit enough for it to be worth the time and effort of making them learn (i.e. is there net benefit)
Assume for the sake of this question that the alternative to making the student learn factoring would be allowing them to quietly chat, hang, and chillax with their classmates, not instructing them on some other valuable skill.
Ignore the direct benefit of passing high school math, they will get to magically pass and move on with their life even if they don't learn factoring.
Non-exhaustive list of potential benefits to consider:
Building of self esteem
Fostering skills related to logical reasoning and/or abstract thinking
Gaining skills/knowledge that will be later built on in university
Gaining prerequisite skills/knowledge for other topics in high school math that actually are useful
Impressing chicks
Learning life is cruel and that they must shut up put the fries in the bag
Becoming empowered to complete geometric calculations on scratch paper while sorting out the dimensions of a bird house they are making
Looking cool for girls
Realizing how fun parabolas actually are once you get to know them
Learning the language of god and comprehending the fundamental nature of reality itself
Getting attention from women
Being culturally enriched by knowledge passed down from their fore-bearers
It builds character
Non-exhaustive list of potential downsides to consider:
Damage to self esteem
Developing an antagonistic relationship with learning and education itself
Paper cuts
Boring and lame (false but included for completeness sake)
Garnering inconvenient amount of attention from attractive females
It's impolite to play God, if He wanted the quadratic factored He would have done it Himself, He's God He doesn't need our help with high school math
Uses up brain space that could be better spent memorizing more digits of pi or mentally simulating imaginary scenarios in which annoying people are hit with epic zingers
The crushing weight of expectations from a society that sees students as nothing more than raw material to be moulded into cogs for the machine
The stifling of creativity
@PaulBenjaminPhotographer skills are important, even rote skills can be! Automaticity frees up brainpower to consider more complicated mathematical concepts/problems without stumbling over the more simple constituent parts