What does this mean? Here are a few thoughts of mine that may be helpful.
This move puts the Codespace "closer" to the repo.
The experience to create a Codespace is streamlined. The button that you choose to clone a repo is now extended to include the capability to create a Codespace.
The experience inside of VSCode is the same. 👍
GH has a page that will show all of your Codespaces. So that experience translates as well.
Microsoft has not commented on pricing yet. Like most Microsoft cloud services, usage of the beta is free. I would expect, however, that the billing will come thru your GitHub account instead on Azure Subscription. I believe that Codespace usage will be allocated similar to Action minutes/month.
If you are not yet in the preview, you can request access here: https://github.com/features/codespaces/signup.