if you had to leave notes possibly for searchers/rescuers then more surfaces are suitable to leave messages on with a pen and a pencil at hand. I tend to think in terms of the advantages of having both rather than the advantage of one over the other.

They are small so I think the added utility is worth the space but realise that even more so than with other items this seems to be a matter of personal taste/habit whether you think the space is justified.