>Hm I've seen sources that say it's only purpose is to secure the plug into a wall, it won't provide ground but I'm not a professional

The post-er said, "if the outlet conduit is grounded," this will ground your connection as well. If the outlet is not grounded, it will only serve as you have commented - it will deliver power and allow your machine to run, but no surges will be diverted to the grounding circuit since there is none.