The 3-million-pound Falcon Heavy can carry as much as 140,000 pounds
to low-earth orbit, almost thrice the payload the Falcon 9 can. It's
able to fly such a big amount to space, since it was designed with
manned missions to the moon and to Mars in mind. According to previous
info from the private space corp, it might try to reland
the rocket's upper stage during the demo flight. It'll be extremely
tough due to the vehicle's weight -- Musk even admitted that the odds of
success are low, but it's still worth a shot.
While it'll be great to see the Falcon Heavy leave for its first journey soon, don't forget that SpaceX and other space companies are known for pushing back timelines. Sometimes, it's to give their personnel more time to perfect their work, other times it's due to unfortunate accidents. In SpaceX's case, it had to push back several planned launches after its rockets exploded. If the Falcon Heavy's demo flight does push through, make sure to keep an eye out for a live stream of the historic event.