For regular commits, sure, but for snap-shotting your work, I think it's fine. The backup branch would never be shared with anyone else, as you'd either push it

For regular commits, sure, but for snap-shotting your work, I think it's fine. The backup branch would never be shared with anyone else, as you'd either push it to your own workspace/fork or to a clone on a mounted disk. For this type of ephemeral backup of code-in-progress, I think storing it in git would be really convenient, because you'd just use standard git commands to find what you're looking for without having to deal with another tool.