I told a few people I was going to post a thread here on why I think hitting into a net is, in many cases, a better way to make changes to your golf swing and to improve, but it turns out I already wrote a good bit about that topic. It's right here, in my "Improvement" post.
But I'll say a bit more about it here. But first, that quote from The Golfing Machine:
Simply put, all too often, outdoors, students get obsessed with making the ball go somewhere. As great as that sounds, it's often counter-productive. The only way the student knows how to hit the golf ball is the way they've always done it. If you ask them to make a change, they're not going to want to because making only that change is rarely going to produce instant results. As in "the next ball."
As dumb as it may be, golfers still think that they're going to get miracle advice. For example, I'm thinking of a certain student I had. He came over the top and hit some big pulls (to clarify, the path wasn't responsible for his pulls - I'm just saying his path was bad, but the face matched up to it). We've seen time and time again that we can change a student's path without severely screwing up the face angle. So anyway, this guy makes a few compensations in his swing, and I know the first thing I've gotta get him to do is to push the ball. So he starts hitting big blocks, which are fine - he's one of the few guys who "rotated the face with the path," if you know what I mean. So he hits 25 pushes, and then I show him how to do something to control the face just the little bit that he needs, and he hits another 20 that way, and leaves happy.
The thing was, this guy had complete trust, and at the end of the day, he could play that push if he wanted and we'd done nothing more. I'd explained to him before-hand that he should expect to hit some big pushes but that would prove that his path had changed, and that we'd get around to showing him how to control the face. So when he instantly started hitting pushes, he was excited about it and it made me look better in his eyes.
Anyway, this guy was rare in that he trusted me... A lot of golfers will say "I'm okay with hitting it worse before I hit it better," but it's simply not true. A lot of golfers will say that they trust you, but you put that white pellet down in front of them and put a flag in the ground 200 yards away, and trust takes a back seat to "I want to make the ball go there!!!!"
Ask someone to swing at 50% their normal speed indoors and you get a swing that's 70% their normal speed. Ask someone to swing 20% outside and you get a swing that's 75% their normal speed. People like to see the ball go: a) far and b) towards their target.
It all goes back to the Golfing Machine quote. Make the correct motions - the ball flight will follow if you have any clue what you're doing. Practicing indoors or into a net lets you focus on making the correct motions. The ball is effectively just there so you're not swinging at air.
Will your swing outside - to a green with a flag and water and sand on a golf course - be different than into a net? Perhaps. But why should it be? If you tend to amp up your swing or do something different, I'd call that a mental mistake, not a physical certainty. Get your mind in check. Make the same swings you make into a net on the golf course. Heck, take the Jack Nicklaus bit to an extreme - pick out a target a few feet in front of you and hit that. Just like a net. Just make sure the target just in front of you is lined up with your eventual target out in the fairway or on the green.