Capacitors do in fact store a significant charge from an AC line. How much will depend on where in the sinusoidal wave the circuit was broken. Anyone that has built/balanced their own Rotary Phase Converter knows this all too well....it scares the heck out of you when you reconnect the caps differently.
The capacitor will have a charge on it that depends on where in the sinusoidal signal it was disconnected. The problem isn't simply reconnecting it to power while it is charged, but the 50:50 chance that it will be charged with an opposite polarity to the instantaneous position of the sine wave.
There will always be some arcing when the capacitor is reconnected because the odds of it having the same voltage as the existing sine wave is low. How much arcing depends on how far apart these voltages are. The greatest arcing occurs when the polarities are reversed. By discharging the capacitor, you minimize the maximum voltage difference between the capacitor and the incoming sine wave.
That being said, I certainly am not going to run down to my shop and monkey around with bleed resistors on such a trivial issue. The contacts on the switch are rated for the use.