I have seen many tutorials about powering the Pi through the GPIO. My question is why do people do it?
By powering the Pi through the GPIO, you lose protection from surges in current and voltage, so your more likely to damage your Pi.
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This is one of those myths.
Certainly many people power the Pi through inappropriate means. Even more use inadequate/inappropriate power supplies and lousy μUSB cables (indeed I cannot find any source of quality cables with guaranteed specifications and have been forced to make my own).
There are many good reasons to power through the power pin on the expansion connector e.g using battery supply and there is no risk if you apply proper engineering practices. Indeed I have seen a Foundation recommendation for such connection.