Question: My current sail has a bolt rope with clew slug. I'd like my new sail to be loose footed... do I still need a clew slug?

Answer: If you have a boom with a slot / groove for the foot bolt rope, but decided to go with a loose foot, you "could' use a clew slug in that groove. However, a clew slug is really to prevent the foot bolt rope from squeezing up out of the groove, so there is really no need for the slug with a loose foot (no bolt rope in foot).

Most loose footed mains have the clew attached directly to an outhaul car, or have the clew held down to the boom using a webbing strap with double velcro, with the outhaul wire shackled directly to the clew ring.

Therefore, the answer is "there is no reason for clew slug as long as one of the other two solutions is being used."