Originally Posted by
badmother
I do not remember exactely what he said, if it was when using the small chainring or when folding the bike there is danger of breaking the der but this mod is important, at least on the der he used.
Removing the bottom of the cage certainly looks important given where the chainring is in the photo relative to the derailer bottom. Without removing it, the chain would be hanging on it. A "fast" fold would probably bend the derailer or mount over time.