Strictly speaking you don't need to run the controller. The Android app can configure APs in standalone mode and update their firmware.
You don't need controller per se to get per-user VLAN assignment or WPA Enterprise. What you need is running RADIUS server somewhere, and controller conveniently provides a basic one (it has FreeRadius underneath, but provides only basic configuration options, so you won't be able to use AD for your users; also do not edit the config manually, any update will wipe your edits).
For guest portal, you need, well, guest portal somewhere. The guest portal is a part of the controller. However, if you need guest portal, I don't see any problem running controller somewhere.
For the rest, you can also run controller on your computer once, configure everything and then shutdown the controller. All the devices will work fine without it.
Edit: word
for the record, most other industry that offer APs that run on standalone will work with all features, or only advertise that feature on the package. For example, you don't see cisco(?) unleashed mode APs advertising guest portal, unless they can do it on unleashed (stand alone) mode.
Unifi is intentionally misleading.