Hmmm... great people, excellent support for new people, and some great stoylines created by the players themselves. I think that'd be a good start for reasons I like SB118 :)
As for practicality... The game runs mainly through Yahoo Groups, so it's e-mail based. I've found that this means I can keep up with what's going on with my crew regardless of location (as long as I have net access :P), and also helps a lot to counter the effects of time-zones - we have players from all over the world working together.
Okay, that's about all I have time to put right now... If you are interested, I strongly recommend you take a look at
http://www.starbase118.net - the stuff on the site should answer your questions, but feel free to poke someone if you have any more querys :)