I guess a benefit is that if you lose your private key nostr:npub1earna05hx6ax38r33h3atmecjzdu547m8suw87w70aw6mlyga4hsqcja5j can restore it for you?

From other comments below I see that nostr:npub180cvv07tjdrrgpa0j7j7tmnyl2yr6yr7l8j4s3evf6u64th6gkwsyjh6w6 sees custodial clients as a way to "keep everybody in check"