If anyone is interested in keeping long-term records and functionality, I'd suggest steering away from anything Google, with their track record of killing things.
Always a possibility. I have no concern using this because:
"Stack can also automatically save a copy of your documents to Google Drive. That way, should you ever decide to stop using Stack, your documents will be accessible in Drive and easy to export. "
Unless Google closes your account for uploading too many, too few or just wrong documents - or, more likely because of some unspecified violation of something.