Many cooks like to sauté mushrooms, usually in a bit of butter or oil, until they are a bit brown. This improves the flavor and texture. And most people add the salt (if they are using it) right at the start of cooking. Turns out that this is not a good idea! Adding salt at the end of gives better results.
Here’s why. Adding salt at the start can draw liquid out of the ‘shrooms, and this liquid will inhibit browning. So, add that NaCl right at the end of cooking. You’ll thank me!
Mushrooms naturally contain a lot of water, up to 90% by weight according to some sources. This makes them difficult to sauté properly because they will give off that water and end up stewing, at least until the water cooks off. But, they won’t absorb more water if you wash them, or at most a tiny bit. Of course, some water may adhere to the gills, but that can be shaken or dabbed off.
Washing is not advised for a few mushrooms whose physical structure makes it impossible to get rid of all the water–morels and lion’s mane, for example.

Your taste buds will give the lie to this myth. The brown cremini have a deeper and more mushroomy flavor than the white mushrooms. Choose based on the needs of your recipe.
On a related note, did you know that portobello mushrooms are nothing more than large creminis?