One good thing about VPNs that allow port forwarding is that it lets you host something without using up your real ports or having it appear to even be at your house. Ex: if you already have something on port 80 but want to host another web server on port 80 elsewhere you could use a VPN to essentially get a separate IP. Or if your ISP does not allow web servers you could use a VPN. They'll just see VPN traffic and not web traffic.
Also a good way to somewhat hide darknet services. Though best bet for those is to host on a VPS separately, but it cna be nice to host stuff at home if you have lot of server/disk resources then just need a cheap VPS to tunnel it out to the internet. Of course the darknet services would be setup on a separate vlan that is only allowed to connect to the VPN. Come to think of it, that would probably be an acceptable way to setup a tor exit node. The more of those, the better, because the government more than likely has a lot so it's best to try to outnumber them.