Let's cut to the chase. Why in the heck would a person want to swing inside out? Well that's a great question. That I asked myself?!? Lol. Laughter will help you live longer, that's what they say. So go ahead and laugh when you can. And if I'm not that funny go ahead and laugh anyway, it'll make me feel better.
Seriously though, let's talk about WHY: let's start with the fact that MOST amateurs swing OUTSIDE-IN. Meaning that for a right-handed golfer the path of the club cuts left across the ball. For most imparting a slice spin on the ball, for some the get their "face" more closed a pull-hook, or pull. You'll run into serious trouble though as the clubs get longer. Meaning that you don't have the loft on them, and when you swing outside-in you're going to de-loft the club and make it hard to create any reasonable launch angle. Unless you make some crazy compensation which also would NOT be good for your long-term results.
The fact of the matter that swinging inside out is NEEDED for most golfers, and will only help you further understand your golf swing, and the feels that go with changing your ball flight. I want to ask you a question.. If you wanted to punch a hole in some dry wall, let's say with a tool, or your hand if you're feeling crazy (but don't do it on account of me). Most spouses wouldn't be too happy! But let's think through this theory if you wanted to apply maximum to a wall, which direction would you hit it? On an angle, or maybe straight on? I'm betting you would go with straight on, as would I. You can deliver maximum force to an object if you hit it straight on. Same goes for the golf swing. If you're swinging across it, you're creating a glancing blow, and the extra backspin will chew up your distance. That it in itself is the simplest and best explanation I can give as to why you should swing MORE INSIDE OUT. Having your path near square or zero is awesome, but many great golfers through history have played with swing paths up to 10 degrees inside out. So if you asked me a range of swing path numbers for great golf, I would say anywhere from 2 degrees outside in, to 10 degrees inside out. With the sweet spot being about 0 or square to 5 degrees inside out.
The swing path is a complicated and perplex beast of its own. One article doesn't cover all of it. But I hope it gives you greater understanding of what you're trying to accomplish and why it's important. Check out the video about if you'd like some more explanation on swing path and one of my favorite drills/practice stations.