[Lingtyp] The purpose of convergence and divergence?

[Ian Joo]

Dear Typologists,

I would appreciate it if you could point to me the literature discussing the purpose of linguistic convergence and divergence.
Do they happen simply because they happen - or do they serve any purpose? Do they bring any benefit?
For example if my lect changes based on to what my neighbors are speaking, it's an interesting phenomenon, but what good does it do? Does it make me more suitable as a neighbor? Does it make it more easier for me to learn their (dominant) lect? Does it facilitate code-switching?
Same about divergence - if a group that split away from a bigger group changes their lect in a divergent manner, then what benefit does it bring? Does it solidate their group identity? Does it help to identify an in-group member?
These questions have been stuck in my head for quite a long time now and I would be grateful if you could provide me previous insights on such questions.

From the Netherlands,
Ian