I use pot right after Unmend for the reasons you stated. Since I use Dark Arts prepull > Unmend > Scourge + Carve and Spit > etc, I'd like to have that Pot going ASAP to affect Scourge and Carve and Spit, and then the rest of the opening rotation along with all the off global cooldowns.

Take care if you're not MTing as this usually rips aggro for a second even without grit.