In the following sentence:
Le scarpe sono ancora in/nella scatola.
Is there any difference in meaning/usage between "in scatola" and "nella scatola"?
In the following sentence:
Le scarpe sono ancora in/nella scatola.
Is there any difference in meaning/usage between "in scatola" and "nella scatola"?
As I noted in a comment, to my ear "in scatola" sounds idiomatic only for canned food (carne in scatola) and board games (giochi in scatola).
I think the general rule behind this is that the preposizione semplice is used for general or idiomatic meanings / set expressions, while the preposizione articolata is used for referring to a specific object.
The same idea appears in English, too: go to church vs go to/into the church. So you would use in scatola when you use boxed in English, and nella scatola when you use in their box in English. In one case it's the general concept of something that comes in a box, in the other you are speaking about a specific box that you can point your finger at.
See for instance item two on this grammar text.