Why use a starter?

Ok first of all I am at work so searching the forums is a bit tough. I have been brewing over a year now, about 10 batches, and have never made a starter. I use the Wyeast smack packs for everything. I have only had one beer, an apple ale with 1gal of cider, have trouble hitting the expected FG. I just tossed a pack of Muntons dry yeast into it. Everyone who has tasted my beers has loved them. Is there some secret Im missing out on? Besides lag periods, what are the benefits of a starter?

Typically, there isn't enough yeast in a standard vial or smack pack to ferment the Wort at optimum levels.

Starters help with lag phase.

The extra cells can help fight off any foreign cells that were potentially present in the Wort.

Starters ensure that the yeast is healthy and viable to begin with. Maybe one day you forget to check the expiration date on your yeast pack and accidently use old unhealthy yeast.

I'm sure there's more reasons, but these are my big ones.

The biggest reason is to shorten the lag period. During that lag period, while the yeast are reproducing, they're also generating byproducts that can introduce off flavors into your beer. Typically those get cleaned up if you give them enough time, but not always. Anyway, with a starter, you build up a large population of yeast before they ever hit the beer, so they spend less time reproducing, thus less lag, thus less byproducts to clean up.

Some side benefits, like mrrshotshot pointed out, are that the shorter lag time gives other nasties less time to take over within your wort, and also let you know that your yeast is indeed healthy before you pitch it into your fermenter.

Good info here.

You guys are awesome. I know this has been answered before but I really apreciate it.

I'd just suggest trying a beer where you make a healthy starter, say 2-3L. Compare to beer direct pitch. Then you'll have your own evidence. I've done this a couple of times and come back to the starter.