What's in a Knead?

Knead time makes quite a bit of difference in the final texture and to a lesser extent taste of the loaf. A long knead will produce an tight, uniform crumb structure since the more you work the dough, the more the glutenin strands are able to bind with one another and create a closely-knit matrix. A short knead does not allow the gluten to organize in this manner so the final crumb is irregular and creamy in texture. If you just look at a baguette cross section vs a sandwich loaf cross section, this difference becomes obvious:

But that's not all. Kneading the dough brings the dough's surface into contact with the air, oxidizing some of the caroteins and other compounds in the flour and causing them to loose their flavor. For enriched doughs, this isn't a huge issue since most of the flavor comes from the fat or milk added to the dough. But for lean doughs like baguettes, virtually all of the flavor is extracted from the flour so preventing oxidation is important when trying to improve the loaf's taste.

If you want improve your bread game and get predictable results even with machines you are not familiar with, you should read a little about short mix, improved mix and intensive mix.

They describe different stages of gluten development. As you mix, you develop and strengthen the gluten network in your dough, which affects mostly crumb hole sizes and flavor as well as loaf size . Of course there are other factors too, but this is a major one. Short mix is usually for large hole breads like baguettes (like in the picture above) or ciabatta, then a couple of stretch & folds are added during bulk fermentation. Improved mix is for your everyday loaf. Intensive mix is for brioche-type doughs like sandwich loaves. 

.You can check the stages by doing a window pane test and see the gluten develop from shaggy and messy to smooth and stretchy (see picture below). There are actually scientifically calculated rotations of a mixer to reach those stages. I believe it is 600 rounds at first speed for short mix, 1000 on second speed for improved mix and 1600 on second speed for intensive mix.
Of course mixing time varies with each mixer and type as each of them have different RPM and mixing "movements". But for example with my KitchenAid Classic those numbers seem to be fairly accurate (usually it takes a minute or two more, but that is probably just my lower quality flour).

In short: short mix leads to the best crumb flavor and the largest crumb holes, but it also requires a lot of manual work during bulk fermentation. On the other side, intensive mix leads to large loaves, tight crumb (small holes) and bland(er) flavor through oxidation. But it requires the least manual work and is therefore preferred in mass production. 
Improved mix is a combination of both worlds, good flavor, less manual work and good loaf size. Not the best, but also not the worst.

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Thanks for that. And here was me thinking the more you kneaded the better for holes as the gluten was stronger/ more developed so retained the expansion within better.  That'll explain why all my breads to date are beautifully tight crumbed when all i really want is loads of holes :)