Sometimes they get lost, and if you kept paper manual for everything you have, you'd need dedicated storage...but, if they were online...
I have a shelf just for that. Every piece of equipment has a manual that I own.
Because it's convenient. There ARE online manuals for many products. They're not "free"...cost is built-in.
Probably are. Not my stuff.
No manuals w/66 BSA I bought, but I now have Owner's/Shop/Parts...thanks eBay. I often read online manuals before I buy new/used...helps with decision/evaluation.
66 Beezer. You need locktite and safety wire before a manual.
Again, I read instructions before buying...helps me decide if product does what I want/need...