I’m glad you asked, OP.
Language is a system, as the structuralists of yore argued. And if there is a paradigm of cases, then people will exploit choices in the paradigm to communicate different kinds of meaning.
Even when those choices should be grammatically incorrect.
The example I have in mind is from Modern Greek. Modern Greek has a vocative, which is still distinct from the nominative in one declension.
The vocative is used to address people. The nominative is used to name the subject of a sentence, which is who you are taking about.
If you use the nominative instead of the vocative, you are choosing to name someone instead of addressing them. That is pretty much the distinction between talking to someone, and talking at them.
Which is, of course, rude.
It is also ungrammatical, but there are two contexts where it is commonplace. The first is the expression ep, kyrios! Which corresponds closely to hey mister! That’s kyrios, not the vocative Kyrie. It is not meant to be deferential.
The second context? It is a context where no deference is meant to be shown to people. Where people are forced to accept that they are part of a machine, and not autonomous agents. And for that reason, people are not addressed, for a request to comply to instruction: they are named, as those who will carry out the instruction automatically.
Being addressed in the nominative is rather popular in the Greek army. Papadopoulos! Three days confined to barracks! Papadopoulos is not going to be shown the courtesy of the vocative Papadopoule. That would involve acknowledging him as an individual…