Note that the snubber allows some current to pass -- this may not be suitable for all loads. Example, LED lights will flash when the switch has leakage like this, because the leakage charges their capacitors, which eventually get up to operating voltage, turns on, flash, uses up the stored energy, repeat.
The snubber doesn't do anything for turn-on, because the contacts are a much lower resistance, they are in parallel, and the lower resistance dominates.
The snubber only works for turn-off, because the contacts go high impedance, in parallel with the snubber, and the lower impedance dominates: the snubber. So the snubber should be dimensioned for the open-circuit condition, which has to do with the wire length and/or inductance around that circuit.
Ideally, you'd use the inverse of this network: an inductor in parallel with a resistor. This is connected in series with the contacts, to snub the turn-on condition as well. This is not commonly done, unfortunately.
Tim