It's a trade-off, for both SEO and users, and I don't think there's one answer that fits every situation. The category level can add information, but it also makes URLs longer, which can be bad for both bots and people. If you have short, descriptive categories that aren't repeated in the product/page names, and those categories mimic your site structure, then I think it can be positive.
My argument was mostly against people adding categories just for SEO benefit (it's probably minimal, at best) or repeating every category, sub-category, etc. to the point of absurdity, causing keyword cannibalization and massive URLs. For example:
www.bobscamerashop.com/cameras/digital-cameras/canon-cameras/eos-cameras/camera-canon-eos-rebel-t3
Of course, that's also keyword stuffed, but I'm exaggerating to prove a point. You can go too far in either direction.
In general, though, I don't think categories in the URL are necessarily bad. In some cases, as Woj said, they could be a positive for users and possible even SEO.
