There are many ways demolition firms bring down a building or structure, a lot depends on the surrounding area and the insurance liabilities. For example, in the picture above, which looks to be a smokestack of some height, its not uncommon to lean it over with charges. I believe that prior to 9/11, in New Jersey two similar storage tank/towers were brought down, and they were both leaner drops, as well as cascade explosions down the body.

for other "Hollywood" events - such as what was shown in the movie Enemy of the State, demolition firms will rig the structure with fuel pots designed to go off in a designed manner to highlight and dramatize the event. this also happens at Vegas implosions where fireworks, flash-bangs, and other fuel glam-bangs are employed.

For 9/11, it was a requirement that something of a diversion be employed - the fuel-laden aircraft - to slam into the buildings and give a "plausible" explanation for the subsequent collapses. If, for example, the buildings just spontaneously collapsed without a plane crash into them, that would have required a massive investigation and explanation to the public. People would have been going "wait a minute," buildings don't JUST collapse.

By having a series of plane crashes and spectacular fireball effects, the public was ready to accept the government version without much critical thinking.