I will weigh in on this because I see some differences of opinion here. I am no means the be-all, end-all of knowledge, but have experimented much and have learned much about meat and its preperation. If anyone disagrees, please give specific reasons and examples to prove your points. I am certainly willing to discuss thsi topic and learn something new.
Meat, be it chicken, pork, fish, beef, lamb, or whatever, contains protiens. These little molecules are very similar in all meats, and even in many grains and veggies. And they all react the same way to heat.
Protiens start to tighten their structure when exposed to any heat above 165' degrees Farenheight. Since they are in close proximity to each other, they also tend to intertwine. The result of this molecular behavior is that juices are squeezed out, while the structure becomes tough and chewy.
To avoid this, whether you are poaching in liquid, broiling, grilling, roasting, baking, steaming, smoking, deep fat frying, or pan frying, monitor the meat temperature. Keep the final temperature at a maximum of no more than 165'.
Obviously, with some cooking techniques, this is difficult if not impossible, and so practice becomes the rule for learning when to remove the meat from the heat. For instance, through experience, I have learned that a great technique for producing fabulous fried chicken is as follows. Dip the skin-on, skinless, bone-in, boneless (it doesn't matter) chicken in egg-wash, then in seasoned flour. Fry in two inches of hot oil until just starting to brown. Remove to a foil-lined jelly-roll sheet and place in a 375' oven for 30 minutes.
I have used this technique for years and it produces chicken so juicy that it squirts you when you bite into it. The timing was arrived at by someone other than me, who taught it to my Mother-In-law, who taught it to my DW, who taught it to me.
With grilled chicken, I just grill it over a solid bed of charcoal, with the lid on, and the vents all closed to the half-open position. I let it cook until my internal clock says to me, "Turn that chicken over!". I turn it, put the lid back on the Webber, and cook it until that same internal clock says, "Take it out. It's done.". I have no clue how I know when it's done. I just do. I guess that internal clock has been set by experience from years of gilling chicken on the Webber barbecue. Again, it's not overcooked, and is juicy so that it squirts you when you chomp down on it. Also, don't add any sugar-containing sauce or condiment to the chicken until the last 5 minutes or so of cooking time to avoid burning the sugar in the sauce.
For turkeys, roasts, whole chickens or game hens, pork etc., I allways use a meat thermometer to tell me when the meat is done. The only exceptions to this is when I'm cooking meat with significant fat and connecting tissue. Then the meat is slow roasted in a moist environmet until it reaches 195 degrees. Then it is fall-apart tender and juicy due to the melted fat and collagen content in the meat. This works for spare ribs, short ribs, shoulder roasts, etc.
So in summary, do not overcook the meat. Soaking the meat in a brine solution adds flavor, but not really any extra juicyness, unless the meat has lost moisture due to dry aging. Thimk of it like this. Each meat cell is muscle tissue, and is in effect a bubble of liquid surounded by a protien membrane. Brining transferes flavor molecules from a concentrated brine solution to the liquid inside to muscle cell until there is an equillibrium established. But that bubble will only hold so much liquid due to its size constraints. Brining doesn't change the size of the cell. It only exchanges the contents of the cell.
Heat, whether provided by dry air, radient energy, deep fat, water, or steam serves to react with the meat and change the structure of its componants. If you want an interesting experiment, take a piece of meat, any kind you want, and immerse it into boiliing water. Let it boil away for a couple of hours, adding water as necessary to keep the meat immersed. Then, remove the meat and try chewing it. you will find that it has dried out and become very tough, though completely immersed in liquid. The protiens reacted to the heat, not the liquid transfering the heat. They still tightned up, squeezing out the liquid, and becoming tough. So once again, do not overcook the meat, and you will be rewarded with great meat.
Hope that helps.
Seeeeeeya; Goodweed of the North