Why is knowing if they find any use in it at all useful though?
Would a better question have been:
A. I find the 5e D&D alignment system nearly perfect and wouldn't change a thing.
B. I find the 3e D&D alignment system nearly perfect and would go back to that.
C. I find the OD&D alignment system nearly perfect and would go back to that.
D. I find one of the D&D alignment systems sometimes useful but would modify it in small ways.
E. I find one of the D&D alignment systems sometimes useful but would replace it with something that wouldn't be classifiable as a 3-way or 3x3 alignment system and might be more verbose on the character sheet.
F. It's garbage, dump it.
We aren't talking about 3E or OD&D alignment. This is specifically marked as a 5E thread.
But on that topic, a lot of people seem to be bringing in assumptions and baggage from previous editions. In 5E we are explicitly told that alignment is not straightjacket, it's not meant to represent every action of a PC, NPC or monster. There's only 1 subclass that I know of (Oathbreaker Paladin) that specifies that they must be evil. Mechanically alignment has no more impact than traits, ideals, bonds, flaws.
According to the PHB alignment:
... broadly describes its moral and personal attitudes ...
These brief summaries of the nine alignments describe the typical behavior of a creature with that alignment. Individuals might vary significantly from that typical behavior, and few people are perfectly and consistently faithful to the precepts of their alignment.
The MM? General idea of default behavior:
A monster’s alignment provides a clue to its disposition and how it behaves in a roleplaying or combat situation. ...
The alignment specified in a monster’s stat block is the default. Feel free to depart from it and change a monster’s alignment to suit the needs of your campaign.
So a lot of people find it useful at least some of the time. I think this iteration hits it about right for me; a quick descriptive tool that can be useful now and then that I can ignore when I don't care or need it. No it doesn't tell me how that NPC was raised or what their attitude is about the color green. Those are details I'll fill in if I think I need them. It
does give me a general starting point and a clue on how to run them when the players do something and interact with NPC/monster in a way I didn't expect.