I had a herp derp moment recently after installing OpenVPN then discovering that Nginx refused to restart because port 443 was 'bound by another process' or something like that. This looks like a pretty easy workaround.
Do note that 443 is typically the web interface for OpenVPN, not the actual VPN port.
I didn't have an IPTables rule allowing the VPN traffic (UDP port 1194) and so OpenVPN falls back to using 443, which triggered the problem. I looked at the workaround and decided not to bother as I didn't really need a VPN, I was intending to use the machine as an Nginx server only.