Think of it this way, you're performing surgery to remove blood from someone, but the tools used, will suck that blood out so fast you can't even blink. If you flip or fumble a little bit, and hit yourself with that tool, bye bye your blood, and you die.

Otherwise, it's just a tool (If you're doing it right) and some knowledge, w/steady hands being the key. Even as an electronics repairman myself, say I'm working on your PC, and I suspect power supply issues. I will NOT take it apart, at all, I won't even bother. I'll just replace it, and test, if the new one works, great, if not, we know it wasn't the power supply, or at least can assume. Either way, it's completely safe to do, as I will not be touching or even looking near capacitors that can hold, a charge still, and discharge it quickly into my body.