This only affect sticks where the stick won't respond to AT commands (identifying itself as a GSM modem) before a PIN has been supplied. In that case network-manager doesn't detect there is a GSM modem connected (modem-manager send AT commands to check if it is a GSM modem and doesn't get the answer it's expecting) and so, doesn't even try to set it up.
This only affect sticks where the stick won't respond to AT commands (identifying itself as a GSM modem) before a PIN has been supplied. In that case network-manager doesn't detect there is a GSM modem connected (modem-manager send AT commands to check if it is a GSM modem and doesn't get the answer it's expecting) and so, doesn't even try to set it up.