Jeffrey Hamelman, widely regarded as one of the top authorities on bread-baking, has this to say in his book "Bread: A Baker's Book of Techniques and Recipes" (p. 8):
Some bakers pull off a small piece of dough and look at the "gluten window" by gently stretching the dough to the thinnest sheet possible (sometimes called the "windowpane test"). This is one way to gauge gluten development, but be careful: If the window is completely clear and the gluten totally developed, the dough has almost certainly been overmixed. Appropriate development does not necessarily mean full gluten development, and as we shall see, many factors affect the amount of time a dough mixes on second speed, and consequently how fully we should develop the gluten in the mixing bowl. If our only goal is dough volume, a lot of yeast and maximum gluten development in the mixer is the method of choice. Maximum volume is one thing, however, and maximum flavor is another, and a mixing technique that favors the utmost volume will also compromise optimum flavor.
("Second speed" here refers to the "kneading" stage in large professional bread-making processes that are done in giant mixers. You run the mixer on low speed first to mix the ingredients, and then on a higher speed -- "second speed" -- to develop the gluten further. Effectively, he's talking about the same thing you're doing when kneading by hand.)
Hamelman goes on to explain what he's talking about regarding flavor. Basically, by kneading or mixing longer, you are incorporating excess oxygen in the dough, which will begin to destroy certain flavor components (particularly carotenoids).
He ultimately recommends a moderate level of mixing (which won't generally pass the windowpane test), and suggests two other options to enhance gluten development:
- Long fermentation times and/or the use of preferments (i.e., part of the dough that is mixed anywhere from a few hours to 24 hours ahead of time, before being added to the final dough), which will add acid to the dough and add to gluten structure.
- Folding the dough during the first rise, otherwise known as the "stretch-and-fold" technique.
I've personally found that stretch-and-folds are by far the easiest and most effective way to significantly increase the strength of your gluten. Wait until 1/3 to 1/2 of your first rise time has elapsed. Then you pull the dough out from one corner, stretch it, and then fold over toward the center of the dough. Repeat from all four sides. Then let it continue to rise. If you want, you can spread 2-4 of these out over the course of your first rise. Even if you didn't knead the dough at all (just mixing it together at first), a few stretch-and-folds spread out over your first rise will usually have your dough passing the windowpane test by the end of the first rise.
These days, I rarely knead much at all. I mix ingredients until they're thoroughly incorporated (which involves some kneading), and then I do a few periodic stretch-and-folds over the first rise. By doing so, I've found my bread often rises higher and sometimes has a better flavor (as Hamelman predicts). There's nothing wrong with some kneading at the beginning, but I personally think the windowpane test is overrated.