First, you need a use-case. It's worthless to have a server just for the sake of it.
For example, you may want to replace google photos by a local save of your photos.
Or you may want to share your movies accross the home network. Or be able to access important documents from any device at home, without hosting them on any kind of cloud storage
Or run a bunch of automation at home.
TL;DR choose a service you use and would like to replace by something more private.
He has actually a point. You need access to your services for which purposes? As long as you are @home, you have access to your services (but those cannot reach outside). You can still browse your photos and likes.
If you are out, it's easier to get a copy of what you need on your device (e.g. passwords) than set up a backup internet connection. (IMO, at least)