Recipes for beef stew generally call for salting and peppering the meat before browning, then simmering for a long time. How is that different from browning, then adding the same quantity of salt and pepper to the liquid, either at the start of simmering or at the end?
There has been quite a bit of back and forth among chefs on whether to salt meat well-before cooking (up to 24 hours) or immediately before cooking. You might find this interesting. The article points out, according to Harold McGee, that a large amount of salt (typically the amounts used for curing) does indeed draw out moisture, however, the small amount of salt used for seasoning allows the cell structure to retain water. The author goes on to test several proteins, none of which are stew meat. My interpretation of this work, for your situation, would be to salt ahead of time. Further, I might try two batches of stew, one where I salted the meat 24 hours in advance, and another where I salted immediately before browning. Why not add the salt later? Well, I think you have a greater chance of drying out your stew meat if you don't salt first.
In addition to salting the meat, you will want to adjust the seasoning of your stew at the end, as water will evaporate and the flavors will concentrate. Seasoning is generally not a one step process.
Pepper is another story. Some people have an aversion to the flavor of cooked pepper, which can take on a bitter note. In this case it can be added at the end of the cooking process.
They are done for unique reasons
Salting meat draws out some of the water content. It is actually also good practice to pat dry the meat before searing. This lets you get a better sear on the meat. Overly moist foods will release their water into the oil when cooking and the water will start evaporate steaming your meat (which is not what you want.)
You pepper the meat (and other spices too) because cooking the meat in oil with them on the surface will cause them to activate and flavor your meat. What I mean is if you add pepper (and some other dry seasonings and herbs) to hot oil it 'blooms'. Adding it to water does not achieve this effect nor does it directly impact the meat.
When you add salt and pepper to the liquid you are seasoning your broth (also important) but it is imparting less of those flavors to your meat.