S-8 registrations are for employee incentive plans. S-1 registrations (and previously S-3) are used by reporting OTC companies for so-called "shelf registations" to register the shares that may be issued under a specific type of PIPE financing agreement.
The use of such "Shelf Share" PIPEs seems to have fallen out of favor as most proved to be toxic floorless convertibles and referred to as "death-spiral financing."
IMO, selling free-trading Rule 504 shares is an even worse form of death-spiral financing.