How much a rocket can lift to orbit is the result of a numbers dance between vehicle thrust and weight. You'll hear a lot of "most powerful" qualifiers get thrown around with the Heavy. When SpaceX says this, they are usually talking about how much mass the rocket can place in low-Earth orbit: 63.8 metric tons, according to the company's website. The only rocket flown successfully that could lift more than that was the Saturn V (a minimum of about 118 metric tons), and the closest challenger existing today is the Delta IV Heavy (28.3 metric tons). The space shuttle, for comparison, could handle about 24.3 metric tons.
How does this rocket fit in to the worldwide launch market? SpaceX is already a leading competitor, with two exceptions: geostationary orbit and beyond-Earth human exploration.
Geostationary orbits match the rotational period of the Earth, allowing satellites there to park over the same spot, which is good for communications, weather, and spy satellites. It takes more power to get to geostationary orbit than low-Earth orbit. The Falcon 9 can already place 8.3 metric tons into what's known as a geostationary transfer orbit, or GTO. These are waypoint orbits where a satellite can "transfer" to geostationary orbit using their own propulsion systems.
But the Falcon 9 is bested in GTO capacity by both the Delta IV Heavy (13.8 metric tons) and Europe's Ariane V (10 metric tons). Moreover, the D4H is currently the only U.S. rocket available for heavy American spy satellites. In some cases, the D4H injects payloads directly into their final geostationary orbits with no muss, no fuss, which is very appealing to the Department of Defense. But look out: The Falcon Heavy can place 26.7 metric tons in GTO, giving it more than enough margin to handle most anything the space industry currently needs.
The D4H is rarely used—about once per year, if that. And some industry experts predict we're actually moving toward smaller, more numerous satellites, rather than giant, one-of-a-kind payloads. So it's possible the Falcon Heavy won't fly that often. But SpaceX still has an advantage on United Launch Alliance here: Since the Falcon Heavy is based on the Falcon 9 and shares the same infrastructure, SpaceX probably doesn't have to spend much overhead keeping it on their launch menu. United Launch Alliance, meanwhile, currently maintains two launch facilities for two different rockets (the Atlas V and the Delta IV).
