Does anybody have recommendations for sites that provide more such instructional videos?
The outputs of the system are fairly innocuous because they are DC at a low enough voltage (max of 12VDC) to not seriously hurt you even if you touch both the positive and the negative of one of the connectors. Now if there was some sort of anomaly and the dc lines were carrying a waveform, then if the wave was a specific frequency to match your body's impedance it could actually affect you. This is kind of akin to a "hollywood" terrorist threat though as it would most likely not happen but if it did it would be tragic.
Also, nobody in their right mind would leave their computer plugged in while working on its internals.
Actually, it's not such a stupid idea, as the case is earthed when plugged in, which can help prevent damage through static discharge. I'm pretty sure my Intel SSD's leaflet actually recommended it. You're very unlikely to get an electric shock from a PSU unless you literally stick bits of metal through the grilles or open it up.
This means only the earth pin is connected, thus earthing your case but without running the risk of having live connected, even if isolated via a switch on the PSU.