My favorite thing hands down is how they handle and use machine metadata though; tags you define in the web UI (or via your infrastructure provisioning mechanism) get shoved onto the machine by zoneinit and then can be used on the machine for configuration, or can show up in the web UI after provisioning (eg. the postgres image uses this to render a "show credentials" button). The service names and what not also can automatically be shoved in DNS (for a simple form of service discovery, although you'll need to implement some form of authentication on top of that since DNS isn't secured), or certain images will automatically trust any public keys you define on your Triton account (I think the SmartOS base-64 image does this, as well as the Debian 9 image).
Unfortunately the documentation for all this is terrible.
EDIT: I left out the other major benefit over some other providers: I can run anything I want, not just supported images. Even if it's something that doesn't fit in an lx zone, they ported KVM over so you can always run, eg. netbsd or whatever in a more traditional virtualized environment. This is great for when you have a few legacy machines left over that aren't using SmartOS or one of their lx- Linux images.