Thanks to Ermal, we now have support for GIF and GRE tunneling in pfSense. Integration with IPsec is coming soon. This isn’t something most people will use, but some like to use gif with IPsec and some need GRE for interoperability with other vendors’ equipment (commonly Cisco in some specific configurations that utilize it).
The use of tunneling with IPsec allows the use of routing across VPN, rather than requiring a SPD match, which is preferable in some environments. It also allows the use of routing protocols across VPN.