If you portfoward it makes hacking you easy, So if you portfoward for a hotel etc its wise just to use it for friends only, If you make it public there is a high chance someone will get annoyed and hack you
Portforwarding is making an exception for a specific port in your firewall. Thus, a program using that port can create inbound and outbound connections. However, most of the time, if you are using a home PC to host a retro, you may get attacked by being DoS due to the fact they can connect to the ports excepted on your firewall.
There are many case of home-hosted retros being attacked by simple "wannabe" hackers by just taking them down.