Not necessarily Github, Github is just one of many hostings for Git repositories, and also besides Git there are other Version Control Systems (Hg, SVN, …), though I guess Git is the most popular.
I use Insync because
- It uploads files on every change, while in Git (and other VCS) you have to manually create a commit and (optionally) push it to the remote repository. So even though it’s a good practice to commit often, it still usually happens not too often, such as every few hours (unless the task is very small and simple), and sometimes it’s good to have more fresh backup.
- In some cases it’s useful to sync/restore files that are not kept in Git repository for some reason, such as local/user settings, input/output files.
- I have several projects that are not synced with any remote hosting even though they use Git locally.
And that’s of course besides other Insync/GDrive features, such as sharing files (documents, videos, zip archives). By the way please add ability to copy direct links 
(Direct links sharing), it’s a very simple feature that would save some time on replacing the link manually or via external tools.