I use Copilot with mostly Claude Sonnet 4.5. Don’t use the autocomplete because it’s useless and annoying. I mostly chat with it, give it specific instructions for how to implement small changes, carefully review its code, make it fix anything I don’t like, then have it write test scripts with curl calling APIs and other methods to exercise the system in a staging environment and output data so I can manually verify it and make sure all of its changes are working as expected in case I overlooked something in the automated tests.

As far as environmental impact, training is where most of the impact occurs, and inference, RAG, querying vector databases, etc. is fairly minimal AFAIK.