Most of the danger comes from not understanding the circuit being tested, IMO. For example, you're testing an incandescent tail light circuit that normally draws 500 mA, and you're using your 150 mA test light. There's no danger there - you're not making the circuit carry any more current than it does normally. If you were testing an LED tail light circuit that draws 50 mA with your 150 mA test light, there may be danger there.
That's why it's important to understand the circuit being tested, and know the draw of your test light. That's also why LED test lights get branded as 'computer safe' - They barely draw any current, and therefore can't hurt anything.
If you have a Premium subscription, there's an excellent video covering this:
www.scannerdanner.com/scannerdanner-prem...xpanded-content.html
For whatever it's worth, I generally consider an incandescent test light to be pretty safe. I can't recall ever damaging a module with one, or worked with anyone who has.
