JM226 said: "no rules to it, obviously. there are also conductors who have been doing the same show for years and still use sheet music. even JRB uses sheet music when conducting shows he's written. so it just all depends.. no "standard" way to it.
Although just because a conductor has the score in front of him (or her) doesn't mean he's actually referring to it regularly. Most conductors use the score as a reference point at best; except in extreme cases (like an assistant conductor being tapped to lead a performance on little-to-no rehearsal), it's very rare for a conductor to be glued to the score while conducting.
"You travel alone because other people are only there to remind you how much that hook hurts that we all bit down on. Wait for that one day we can bite free and get back out there in space where we belong, sail back over water, over skies, into space, the hook finally out of our mouths and we wander back out there in space spawning to other planets never to return hurrah to earth and we'll look back and can't even see these lives here anymore. Only the taste of blood to remind us we ever existed. The earth is small. We're gone. We're dead. We're safe."
-John Guare, Landscape of the Body