Meter probes are oh so shiny and conductive but they also like to slip as well as touch other parts you don't want touched. This sort of unwanted touching often leads to nasty sparks and subsequent release of the "magic smoke" form your components.
It may seem "duh" but wait until it happens to you! Things like vintage power output transistors and old chips are expensive to replace. Shorting an output transistor induces big current flows through other parts resulting in collateral damage. One slip can result in multiple burnt parts.