Plywood will always have some variation in thickness. So woodworkers will usually overcome that by making not only rabbets/dadoes, but also tongues.
But when you're working with slotted plywood, such as the shelving in the image below, how can I deal with that? For long shelves, a single piece may have thinner and thicker sections, so different columns would have to have different slot widths. This seems a lot of work, even for someone working with CNC (which is not my case).
And coming to a subject that to me feels a lot like an urban legend: is it really a no-no to run plywood thru the thickness planer? If I am only removing wood from the outer layers and the machine is not hitting any glue, my guess is that there shouldn't be a problem. But woodworkers in most forums I've searched will advise against that, so I guessed I'd better ask again.
Edit: the picture comes from this tutorial, and it was built with a CNC and the author did state it was necessary to sand some of the slots to get a nice fit.