If you live in a town and use your bike to commute then filtering isn't optional, if you don't filter you might as well be in a cage.
Why sit on a bike getting soaking wet waiting in traffice queues, filtering can be done safely, be alert, learn to read the road and you get a sixth sense for cagers that are about to pull out.
Also I find that lights on full beam only when the car traffic is stationary helps reduce the amount of doors, fags and gob that hits you.
Over the years I have had fags, gob, various fruit, banana skins, spew, all sorts of rubbish, people and animals come flying out of car doors and windows either just missing me or testing my brakes and the odd strike - lit fags are my pet hate, had 'em bounce of the visor and off my body several times - that always ends in a confrontation as it's bloody ignorant.