If someone robbed your phone, maybe he could not use your phone because of your setting of fingerprint or some security policy, but he may use your sim card to get some information of your email or other account.
Not sure about how much benefit the criminal could get from that. Although I think it is not efficiency, but one of my friend meet that and his qq mail account is also robbed.
Then how could we open the sim pin protection?
For android: setting->security->sim pin
For iphone: setting->search “pin” then you can get it.
What’s more, the original pin code of China mobile is 1234, of ATT is 1111.