Packages: why a manager?

[PeterWhittaker]

I’m a long time vim user and this is something I still struggle with: sure, I can use a package manager, but why should I, given vim8? And what criteria should I use to evaluate the various PMs?

(Great doc, btw, learned a lot… things have changed a great deal since I started with vi 32 years ago and returned to daily in depth vim after a 20+ year hiatus.)