They are only honey combe to give the product enough strength, together with lightness, to function where it is constructed of a material with an inherent low strength. Plus of course to save the maker material and associated costs.
Its not a design attribute other than in those respects.
If used open side down it then partly defeats the load spreading using a pad at all aims to do and as already pointed out could so easily pick up soil debris, partly negating the weight saving.
Used, open side up then it is more likely to get water build up but that at least is more readily removed.
I suppose having them makes a different on site "statement" to those that use other things does.
I am in the use a bit of suitable wood camp. Certainly not a bit of pallet plank as these tend to be cut from the lowest quality wood with a high probability of having poor cross grain strength.
Decking though that inherently ought to be reasonably strong for its intended duty, or better still thick marine ply or even exterior [roofing or shuttering] ply make for a way better choice.
These can be made and finished neatly, doing that and using them, where they exhibit some neatness and finesse can also make its own "statement", plus for those into DIY for its own sake give making them some pleasure.