When making a cold deli meat sandwich or a burger, does layering the solid ingredients and condiments in a different order change the taste or mouth-feel? If so, how and why? Are there reasons to prefer one order to another?
Yes, it can change the taste quite significantly.
Here's an easy experiment that you can do:
Mouth feel is affected as well, but not quite as dramatically.
Absolutely! I have had great results with tomatoes directly against the cheese. I can't quite put my finger on why, but no matter where else I've tried putting the tomato slice it just isn't quite as excellent as right up against the cheese (the cheese being right up against the bread in this example (separated only by your favorite choice of lipid =) ))
The timing of its production in relation to its intended time of consumption accentuates the difference that the ordering makes: For example, if keeping a sandwich in a sack for lunch later, I also have had great results putting the lettuce and/or spinach in between solid meat components instead of against the bread, a process which prevents the bread from getting soggy. (Of course segregating the lettuce in a separate plastic bag until lunch time is also an option.)
Aside from my experience, I suppose the fact that I rarely get strange looks from sandwich artists at delis or Subway in regards to any such special requests such as "could you please put the olives under the meat" can be a testament to their understanding that peculiarities such as this are part of the sandwich experience.
Also, if we really zoom in to the elemental level, and observe our food as the combinations of complex chemical compounds that they are, it would stand to reason that the interaction of any given ingredient with any other particular ingredient would vary at least slightly from its interaction with any of the other ingredients, and thus in all likelihood there would at least be some minuscule difference no matter how you changed the layering of your ingredients.