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Disclaimer: I have no formal electronics training.
I am reading this book: Raspberry Pi Zero Cookbook 
Here's the paragraph from that book that's got me confused:
The Raspberry Pi documentation allows up to 2.5 A for the Pi's power supply, in case you don't want to use a powered USB hub. For this cookbook, we will start with a powered USB hub but work toward low-power and low-profile solutions.
I was under the impression that, from an abundant supply of amps, a device will draw only the amps it needs. But the first sentence above implies that you should not connect a power source to the Zero board that is more than 2.5 amps. Can you please set me straight?