Thought this was too good to not post.
Toilet etiquette appears to be an important part of ANA’s (All Nippon Airways) policy — the airline had previously asked passengers to use the lavatories before they board flights so as to reduce the overall weight of the plane, which would ultimately be better for the environment as it would mean less fuel usage. – Original Article
What we can learn from this is that your bodily waste is calculated into the total weight an airplane can carry. So remember, excrete before you fly. The Earth may be depending on it.