Even very small electric shocks can result in people falling off ladders, with consequent injuries (just as can non-electric 'shocks' - such as creeping up behind them and shouting "boo" in their ear!).PS if you search YouTube some guy actually set up a system to give himself shocks, it seemed even at around 20mA it was very painful, so an RCD wont save you from falling off a ladder.
If you're unlucky (and/or have a pre-existing medical problem, of which you might be unaware), 20mA could kill you.
Kind Regards, John