This service wouldn't be useful to me because the number reputation seems poor.
Actual delegation would not rely on pooling numbers for increased user per SIM card. It's one client per SIM card.
Mitigating account lockout risk across lots of clients. Separate SIM for each client, having account lockouts are unacceptable. Yes, I've had problems with no recourse.
Immensely useful services like this without which for instance people would not be able to scrape social media services at scale.