An employee needs to be compensated for their work. If that's in the form of salary or equity, that's your business. However, you need to be compensated, somehow. Otherwise, it isn't work, it's charity. Non-deductible charity at that.

If someone is asking you to work for nothing (no pay, no benefits, no equity), you need to walk... no run... away from that deal.

This isn't even mentioning the fact that the company would open itself up to IP issues if they weren't compensating you. Let's say you came up with some killer code to do something that the world needs. Who would own the IP? The company that didn't pay you? You're not an employee if you aren't compensated - it isn't work for hire. So, now they have a problem.