Some users have recently had their accounts hijacked. It seems that the now defunct EVGA forums might have compromised your password there and seems many are using the same PW here. We would suggest you UPDATE YOUR PASSWORD and TURN ON 2FA for your account here to further secure it. None of the compromised accounts had 2FA turned on.
Once you have enabled 2FA, your account will be updated soon to show a badge, letting other members know that you use 2FA to protect your account. This should be beneficial for everyone that uses FSFT.
I don't know. Why did you or your organization create a sub-interface?
If your outside interface needs to support more than one VLAN then you have to create sub-interfaces for those VLANs and apply policies to them...Maybe you want TCP port 80 allowed through on one VLAN but not on the other...
The question "why" can only be answered by knowing your setup and your requirements. If you figure those out you'll figure out why...
I have looked into this a bit more and the only reason I can see that this is done is so you can easily move the config of the interface to another interface.