Startups used to face difficult choices about when to invest in large and lumpy assets such as property and computer systems. Today they can expand very fast by buying in services as and when they need them. They can incorporate online for a few hundred dollars, raise money from crowdsourcing sites such as Kickstarter, hire programmers from Upwork, rent computer-processing power from Amazon, find manufacturers on Alibaba, arrange payments systems at Square, and immediately set about conquering the world.