Envelope etiquette

I've noticed that I automatically write in small writing on small envelopes, and big writing on big envelopes. In fact I like to use big fat marker pens when writing on A3 envelopes for extra effect.

Is this strictly necessary? Presumably the postman can read small writing just as well whatever sized envelope it's written on. I suppose it just looks a bit silly: A teeny weeny address, lost and alone in a vast desert of brown paper. And if your address gets lost, then what hope for the actual parcel once it is sent into the abyss that is the Royal Mail?

No, I think I'll stick with my chunky writing, just to be on the safe side.