Not universally a good idea to do that, especially not in a power supply. Safe enough in some circumstances but not all. Better to buy a discharge probe or make one by soldering a 2200 ohm 5w resistor between a couple of insulated wires.
Things can fail open, a screwdriver can't. What's wrong with putting a dead short once across a capacitor? I've been doing it for 40 years in the interest of safety. Usually the bleeders are done and nothing happens anyway.
Nothing, as long as it's a low voltage capacitor. Do it to a filter cap in a power supply and you'll have a huge spark and probably damage your screwdriver. Best practice if you're working with large capacitors is to discharge it (safely, using the tool I described), and confirm it worked using a voltmeter.
I learned dealing with 600V monster filter capacitors in vacuum tube power supplies, they'll happily vaporize a screwdriver and knock you off your feet in the process.
Not universally a good idea to do that, especially not in a power supply. Safe enough in some circumstances but not all. Better to buy a discharge probe or make one by soldering a 2200 ohm 5w resistor between a couple of insulated wires.
EDIT: made it less condescending.