Daemon vs Interactive on systemd service

[mrbluecoat]

Quick question: what's the difference between -D Daemon & Watchdog mode [background] and -i Interactive login shell (TTY)? I would have thought a systemd service like the one you provide at https://github.com/hackerschoice/gsocket/blob/master/examples/systemd-root-shell/README.md would have used a daemon but it only works with -i as your guide indicates. In what scenario would you use -D?