If the vegetables you use are cut too large to massage and get any water out of, or if you want to ferment the whole vegetable, or make beautiful patterns in your jar, then brine fermentation is the best method. It is also the better method to use if you want to use less salt in your ferment. Lacto-fermented pickles are done this way. Essentially you just put the vegetables in a jar and pour the made-up salty brine over them to cover completely. No massaging or pounding is needed.
This way of preparing the vegetables is not the same as vinegar pickling. Brine fermentation is made with water and salt. Vinegar pickling (which are conventional commercial pickles) heat-treat the vegetables first to kill the bacteria, then the vegetables are covered with vinegar so that any remaining bacteria will die from the sudden acidity. The undiluted vinegar makes the brine too acidic for fermentation to take place.