With the let’s encrypt addon you will only have https access to Home Assistant. So when you contact it from outside everything is fine. But when you try to access it locally Home Assistant doesn’t react anymore on http, so you have to use https together with the IP-address which is not really possibly as many browsers don’t let you do it. The ssl-certificate is only for the name and can not be for the IP-address which is clear.
If you use Nginx you can have the outside traffic via https and the inside traffic with http. This was the main reason for me to use it.
Also you only have one port forwarded via your browser and Nginx handles the names to forward them to the different devices in you local network. And you only need to remember the names and not any port from outside.
So you can have:
ha.bla.blubb.wherever for your Home Assistant
nas.bla.blubb.wherever for your NAS.
mac.bla.blubb.wherever for your Mac.
pc.bla.blubb.whereever for your PC.
lms.bla.blubb.wherever for your Logitech Media Server
etc.