Author makes this point in a related post: At a glance this “feature” seems like an incredibly bad idea, as it allows possibly unknown information to propagate

Author makes this point in a related post: At a glance this “feature” seems like an incredibly bad idea, as it allows possibly unknown information to propagate blindly through systems that do not understand the impact of what they are forwarding. However this feature has also allowed widespread deployment of things like Large Communities to happen faster, and has arguably made deployment of new BGP features possible at all.