Does breathing on your glasses help with cleaning?

It depends. Your exhaled breath is about 37 degree C and 100% relative humidity. If the temperature of the lenses are less than 37 degrees then water from your breath will condense on the lenses. This water is nearly pure (distilled purity) and can help dissolve any dirt, film that has attached to the lens.

But if the lenses are hotter than 37 degrees, you get no condensation, so breathing on the lens doesn't help. In this case just lick the lens.

Yes , the air we exhale contains a very high percentage of water vapour which condenses upon contact with the glass. Thus when a tissue is used to wipe it, the dirt comes off easily as it is generally soluble in water.