Like steam
Every big site has this, makes being keylogged or scammed and people logging into your acc impossible (weak pw etc)
Ofc you could have the option to turn it off
Same thing if people forget their passwords, if u got your phone linked up and got access to your phone then its much easier to recover your account then having to email admins and show 4520942 proofs you owned the account.
+ If people also do illegal shit down the line with their phone numbers easy track
I only see benefits, idk how this not been added yet.