IMHO A large majority of marinades are much more effective as flavorers than as tenderizers. Acids that are present in vinegar, citrus juices, wine, whiskey, beer, milk etc. etc etc, have somewhat limited tenderizing effect. The real success in rendering meat tender depends more upon selection, proper cooking methods, and temperatures.
They do work well however to change or disguise the flavor of meat. In other words, if you don't like the taste of what you have, marinate it. If you do, then don't. Just season and baste (if needed) during the cooking process. They do work well on gamey meats, fowl , and fish. Personally, I very seldom find a need to marinate.
Have Fun & Enjoy!