Surely engine oil will fling off, or wash off in rain, unless you have a constant oiler fitted?
I always lube it after ride, allowing most of the excess to drip off so theres not really that much left to fly off and any that does find its way on to bodywork etc can easily be removed with a cloth unlike spray on lubes which need degreasents to shift.
Guess its down to personal choice and any lube is better than none
Talking of which. I saw this lad on a 125 the other day who's chain was as dry as Gandi's flip flop's. When I suggested he lube it he replied that he didn't want to as it would make it slip........ I gave up at this point