Let me give a specific example. A week ago I wanted to set up a hunchentoot (lisp) web server, which involves starting a lisp instance, running some sort of setup lisp code, and leaving it running on some console somewhere.
Various Internet searches gave me 50-60 line init scripts for old versions of Ubuntu. These scripts were long and opaque and probably not even close to something that would run on Fedora 18. They relied on the detachtty tool (a minimal screen-type program) and did some sort of $PID dance around this. I wanted the server to restart whenever I killed it, so that I could reload the setup code that way. (Also I kept accidentally killing it by hitting Ctrl+D into screen.)
There's nothing out there about using hunchentoot with systemd. So, with maybe five minutes of searching manpages, I wrote
Description=Run sbcl webserver session on a screen tty
After = syslog.target network.target
Short, simple, clear, works correctly, tells me when things go wrong, etc, etc. I can connect to screen and hit Ctrl+D to reliably restart the server. It never hangs or gets out of sync or leaves ports in use or files locked.