“we mentioned this before how it being how it’s been used before by Ukrainian side is they basically do do kind of like a decoy attack using rockets... overloading anti-air defenses, and once the batteries’ rockets are exhausted, you shoot with the HIMARS system.”
Another aspect of that, is that by firing the decoys (or just enough actuals), you force the Russia Air Defenses to fire, thereby revealing their positions, so that you can fire on the Air Defenses themselves.
Suppression of Enemy Air Defenses (SEAD) is characteristically one of the opening combat actions of an Operational Plan.
Those high value, high altitude air defense systems are few in number, and very long lead time to produce. Once those in the region are destroyed (or stop responding, out of fear), then it will be open season on Russian targets, with the longer range of the Artillery now in Ukrainian hands.
They likely have multiple positions to quickly move to - however, many of them, if not most, are located inside Russia.