What [MENTION=39487]mjbphotos[/MENTION] said. Just use a send if you want to create a parallel/copy of a track with different FX. Simply duplicating with no difference, save PAN, perhaps, does nothing.
And, sometimes your duplicate track+FX can make things sound thinner if you manage to get some phase cancellation.
Re-tracking/recording, playing/singing the "same" thing, though, is a technique some folks use. Since the new track can't be precisely identical, it gives you all those things naturally, i.e., that futzing with delays, chorus, etc. on a duplicate track are trying to do. Of course, it requires a bit more performer talent (IMO), so might not be an option in all cases.