❓ Why it could be a bad idea to "prevent marking and allocation in shared pages"?

This question is extracted from a tweet of Jacob Matthews

About a year ago I started trying to improve Ruby’s memory usage by preventing marking and allocation in shared pages. I wasn’t really sure it was a good idea but the Instagram engineering team have done basically the same thing but for Python https://t.co/sgeqVApQSS

Why it could be a bad idea to "prevent marking and allocation in shared pages"?

...