An F-35B test aircraft completes the first-ever vertical takeoff (VTO) at NAS Patuxent River, Md., on May 10, 2013.
While not a capability used in combat, VTOs are required for repositioning of the STOVL in environments where a jet could not perform a short takeoff. In these cases, the jet, with a limited amount of fuel, would execute a VTO to travel a short distance.
The F-35B is actually only STOVL and not VTOL, like the Harrier. When the F-35B or the Harrier have weapons or external fuel tanks attached, they are too heavy for a VTO. That’s why they are only classified as STOVL and hardly ever perform a vertical takeoff. When they takeoff from carriers, they do a short takeoff instead of a normal takeoff (because the F-35B doesn’t have a launch bar) or a VTOL, because they usually are carrying weapons or fuel tanks and are simply too heavy.
Source: YouTube