240V shocks are rarely fatal. Potentially fatal, unpleasant and certainly not something to court. It's all about the amount of current they can put through you and particularly across your heart. e.g standing up in the bath and fiddling with a faulty light bulb dripping with condensation would be extremely dangerous, but standing on a dry floor in rubber soled shoes with dry hands and feet you might feel a tingle fiddling with the same bulb.
Another danger is the involuntary reflex from a shock which could throw you off a ladder or throw your hand into the way of machinery. There have been horrible accidents caused by non-lethal shocks.
I must admit that I've never found it necessary to prod around with a meter in power tools connected to the mains. Most faults you can find by looking or pick up with a meter on the continuity range or a battery and bulb. A switch conducts or it doesn't and it shouldn't matter whether you are testing it with mains driving 3A into a power tool or low voltage from a battery and bulb or the continuity range on a meter. So as the meter or battery and bulb are completely safe and mucking round with things connected to the mains is potentially lethal and the effectiveness of the test is the same, go for the safe option.
