My ideal is that I use it as my "home base" and everything else is a "peripheral" that checks back in one way or another.
The big things are:
* Music Player Daemon - It has access to my whole music and podcast collection, whereas I only "check out" a subset of this onto my phone at any given time.
* Podcast downloader - I used to have this. I wrote it myself. I got tired of the problems that kept coming up so I turned it off. But, I got recommended a replacement. I'll try it out at some point.
* Gitolite - I highly recommend this one for anyone with this use case. It's a git repository host, for when you don't want all of your business on Github. You can create however many repositories, you give it however many ssh public keys, and you configure which has access to which. The main interface is a special admin repository where you add the pubkeys and configure the repos. For my "home base"/"peripheral" model this changed everything for me, especially since I use QubesOS on my laptop where I'm working in multiple VMs with different ssh keys.
I eventually want Sandstorm.io and OpenHab, but I'd probably want a separate machine since I think that stuff wouldn't be in the Debian/Ubuntu repos.