My damage speed potions immobilize many creatures (though not NPCs) in both OB and SI. Even though the duration is 3 pts for 10 secs the effect lasts much longer (permanently, I believe). Indeed, affected creatures lower their weapons and don't attack, meaning I can just stand there and hurl fireballs at them. The UESP wiki said: "If you can damage an NPC's Strength to zero, they will be frozen in place because of their zero Encumbrance. This can also be accomplished by Damaging Speed to zero."

Whether this was intended by the devs, or an exploit, it comes in handy when there are multiple enemies, or I just don't feel like battling a powerful opponent.

Most interesting, thanks for the revelation