I look at it like this.. elves do not sleep no. They enter a reverie. Drow on the other hand, have to sleep, as I heard it described "They cannot deal with their pasts well enough to relive them day after day without driving themselves to complete and utter madness" which is what reverie is. When a elf 'sleeps' (reverie) they are in a light meditative state in which they remmeber and relive everything that has happened to them in their life. If an elf has say.. a traumatic past, or is say.. a murderer, etc... then yes, they can and do sleep, to rest and avoid the memories. I hope that makes an inkling of sense.
