Re: Benefits of plywood boxes to wooden crates?
Hello and welcome to the forums!
Your question is a difficult one to answer. First, you're asking about boxes vs. crate which, technically, is apples and oranges. 'Boxes' are for lighter and/or smaller items while 'Crates' are for heavier items. I won't go in more depth because I don't think this is the basis of your question.
Assuming your asking about boxes and you're only asking about closed containers, then you have to consider the difference between the base and the cap. Since you can mix-and-match bases, I'll just concentrate on the cap.
Generally a plywood box gives you a better strength to weight ratio. Also, since plywood is an engineered wood, you get a more consistent and measurable strength than you would with a lumber box.
Lumber boxes are often faster to make but since you are working strictly with lumber, you are working more at the whim of the wood. You can get more splitting and may have to pick better boards than you would with plywood.
Working in the range of containers that are strictly and clearly boxes rather than crates, a specification plywood box can hold up to 1000# while a somewhat similar lumber box can only handle up to 400#.
All the common styles of plywood and lumber boxes were designed in the 1930's or earlier. Since then labor and material cost have changed drastically so I wouldn't look at them evenly when considering a project. In general, I think most people in the US start by considering plywood then use lumber if there's a good reason, such as if the container is less than 11.5" high. That's a REALLY general statement though and many people may disagree.
When it comes to crates; I don't think I've ever seen a lumber crate made in the US except for open crates. More often you find them in lesser developed countries due to the higher cost or unavailability of plywood.
The best info I can provide about the rest of your question is that, again, plywood is an engineered product so its performance is more measurable. When considering issues such as puncture resistance or shock performance, you need to consider the load, modes of transport and the size of materials used. Also, when it comes to shock, consider the effects of vibration.