I think that service like PAMM account is relevant for professional traders who, it seems to me, moved to a new level of trading.
These are advanced features for managing accounts and generating more income.

My thoughts are straightforward. It's just a mean for those who want to earn some bucks by managing accounts of various traders who are apparently less advanced than these guys.
And the most important thing that it's beneficial for both parties involved in the process. Afaik, PAMM account is quite popular among seasoned traders and it's cool such reputable brokers as the fxpro offers access to it.