Decreases what info Signal needs to collect and retain about a user. When using an SMS verification as a proof, Signal needs to log the phone number, because if they didn't, one spammer could use one phone number to create 10^99 accounts.
When using payment as proof, they can verify that payment occurred, validate the account and then immediately forget about the transaction. One spammer would still have to pay 10^99 times to create that many accounts.
When using payment as proof, they can verify that payment occurred, validate the account and then immediately forget about the transaction. One spammer would still have to pay 10^99 times to create that many accounts.