The only time I could see myself using this is in the following scenario;

1. Browsing repos.

2. See a quick fix I could make (like a typo)

3. Open up the code space view, make the change, add and commit it.

For my daily needs I would never replace an online IDE with my local IDE. I see no value in doing that. My concern would be for when github has a service outage. I am without my IDE until they resolve the issue? With a local IDE I can just continue to work on my branch and push it when GH comes back online.