The concept of "extra" money

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Here's something I've always struggled to understand: 1) What exactly do websites mean when they say you could make "extra" money? On what basis is the money "extra?" 2) If anything, the money is NOT extra, coz we're likely to spend whatever loose change we get on paying for the electricity that our computers consumed while making those cents. In effect, the money's not extra. It's just required to pay for the costs we incurred while making it. 3)If someone is willing to slave over a computer for hours just to make a few cents, then any money that he or she makes is badly needed and cannot be considered as "extra" in any way.