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Spending more money to deliver in less time can make financial sense. A high-tech doodad that will be obsolete in 2 years can't afford a delay getting to market. The sales you make could add up to more than the premium you have to pay to finish the project earlier.
Crashing is the term project managers use for shortening a schedule by throwing more resources at tasks. It's not as dire as it sounds, although it sometimes describes what happens when a horde of people try to work on the same task. To the uninitiated, crashing seems like an easy choice. If two people can build your website in 12 weeks, then four web developers should wrap it up in only 6 weeks, but it doesn't always work out that way. (And sometimes crashing doesn't work at all. The box on When Crashing Doesn't Work explains why.)