Why do frozen vegetable packets advise cooking from frozen, and should I follow that advice? Packets of frozen vegetables often say "cook from frozen" or "do not defrost" in the cooking instructions. For stir frying at least, many people recommend the opposite, such as in this question. I can understand the logic behind defrosting, but the recommendations don't explain why I should trust them over the packet directions.

Why do packets say "cook from frozen", and if I'm not supposed to follow that instruction, why not? Is it based on a myth? Is there a legitimate problem with cooking thawed vegetables that can actually be circumvented to achieve even better results?

I'm particularly interested in stir-frying mixed vegetables and baking french fries but this can apply to other methods of cooking too.
Well, "cook from frozen" comes with instructions on how to cook from frozen, on stovetop or microwave.  So their results are probably best for those methods.

Stir frying is a different process, so, unless they have stir-fry specific instructions, you should take the "from frozen" instructions to be specific to the methods and instructions given on the package for preparation, not necessarily an admonition for all types of preparation.