On the https://screenscraper.fr site, there's a list titled "Server" in the upper right of the page. There, you can see the current CPU workload in percent. If the load gets too high, the green checkmarks will go red to show that these users will be blocked from scraping until the load goes down. Non-registered users will be blocked first, then registered, then (maybe) contributors.
So, I guess registering will get you blocked later. But I'm not registered there so I can't tell you for sure.