Cooking

Never use salt and soy sauce in the same dish. Soy sauce by its very nature is very salty. Use it sparingly, and it does add a wonderful umami element to your dish. Works great with rice noodles, chicken, beef, pork, veggies, and is complimented very nicely with sesame oil, shaoxing wine, rice wine vinegar, and hoisin sauce. Chinese cooking is a complete game changer and it's so damn easy.

Take a chicken breast, put it in a ziplock bag with some soy sauce and pop it in the fridge overnight.

The next day, cut it up into kabobs, grill, put on an onion bun with peanut sauce, hoisin sauce, sweet chili sauce, shredded cabbage (green and purple), shredded carrots.

You're welcome!

Use soy sauce like salt, and add it late when salt isn't an important part of the cooking process to prevent oversalting

You always need to salt each element individually to get the correct salt level. When you are cooking most vegetables you add the salt on top when you first add it to the pan. Same with meats but those usually get some salt earlier or as part of the marinating process.

While soy sauce is a source of salt it is more importantly a source of glutamate which is a flavor enhancer. Other items such as anchovies, mushrooms, miso, kelp, etc. contain glutamate naturally which was refined into MSG. MSG is just the crystalized form of naturally glutamate from kelp. I use soy sauce usually when things are simmering or as a finishing touch. I usually add it right at the end after adding my finishing touches of an acid. If your food tastes flat it usually missing an acid first before adding more soy sauce since you should add only a few tablespoons or so to most dishes.

Soy sauce does have lots of salt, and you can sub one with another if you so desire. It won't be healthier, but it'll taste different. From my experience the ratio is around 1 tbsp of salt = 8 tbsp of soy sauce, but keep in mind that this varies a lot depending on the soy sauce brand (cheaper ones tend to be saltier).

Personally I avoid subbing all salt in a dish with soy sauce, because the taste of soy sauce gets a bit too strong, and sometimes it introduces too much water. (Except obviously if the dish works around soy sauce, like yakisoba. But then that's not subbing salt with soy sauce, it's simply using soy sauce.)

What would it make more sense? to add the soy sauce with the other ingredients before the mix boils, while boiling or only to add it before serving?

Either sounds fine for me. It depends on what you want to achieve - add the soy sauce before boiling and the ingredients will get salted through, add it before serving and you'll get some contrast.

I cook mostly asian food at home, and a lot of the dishes I make have sauces that are soy sauce based. I usually add it around the second half of cooking time, after cooking the meat/protein and mixing in the sauce ingredients (soy sauce, mirin, sesame oil, etc.). As the other comment said, be careful with the salt as soy sauce is already salty to begin with. I usually season with garlic, onions, and pepper only as the soy sauce takes care of the saltiness.

I have yet to notice anythig different about the time to pour soy sauce in a dish. In any case, soy sauce first, then salt.
Unless you happen to have made a soup that taste bland (we all make mistakes), then a dash of soy sauce can help.

Most East Asian recipes that I have made include soy sauce as an ingredient in some form. That doesn't mean that soy sauce is only for Asian dishes. I've made steak fajitas and steak phillys with soy sauce as well.

I use tamari (soy sauce?) or miso in place of salt often. People love my cornbread. The amount of sodium is the same on my case, and if you tell folks they won't eat it but will love it otherwise (but clear food allergies first!).