Multiple SSL VPN server instances with separate certificate an encryption setting
A firewall config lives for many years. So, after a few years, the certificate and encryption settings of the ssl vpn server aren't up-to-date anymore.
At the current state, if you change certificate or encryption settings, you'll have to redeploy the ovpn-files immediately. The old client settings and certificates become invalid.
But with multiple server instances you could migrate the users with legacy settings to the new instance next to one another.