We only do this if it's essential to protect the food we're sending you. For example, mushrooms or tomatoes get squished without a punnet around them. Other produce, like green leaves, lose moisture very quickly, and need to be put into bags on the farm to prevent it from drying out.
We don't make any assumptions, though. We'll always look at the variety before deciding to use plastic. For example, some of the more robust tomatoes / gourds are fine in paper bags.
We are constantly looking at the way we package our produce and are introducing non-GM biodegradable plastic for all our punnets and bags. But, as of now we are using re-usable zippouches for packing fresh fruits and vegetables.