Is smoking battleships worthless?

As a DD player, other DDs and CAs ask me to smoke-screen them, but never BBs. Whenever I proffer smoke to BBs player, they always decline and say that smoke for them is useless. But why? Is it worthless to smoke BBs?

Like what you said, most of the time it is worthless to smoke BBs since their gun penalty range doesn't let them hide in smoke.

If not, when ought BBs be smoked?

Though it is useless most of the time, it would be useful in this scenario:
Smoke BBs that are dying to let them hide in the smoke and heal up with their repair party.
(Of course, tell them to stop firing in the smoke and heal up.)