To be clear: The PV Array "earth ground" refers to a grounding cable/rod system from the metal racking and the PV panel frames. This needs to be earth-grounded and the important thing that is not really that obvious looking at a PV panel, the aluminum frames are anodized aluminum, and this coating is actually a rather good isolation from the base aluminum. Thus the use of WEEB washers(look them up). Under the NEC the Earth-ground for the PV array "may" be separate from the electrical earth-ground of your electrical system, OR it can be the same earth-grounding system. Often the choice boils down to how far is the PV from the rest of the electrical components? ie hundreds of feet away out in a field may lead to using a separate Earth-ground rod/cable for the PV frames and racks. There are many discussions on this forum about lightning and the potential to unintentionally invite a strike via the PV frames/racking and thus some choose to go with separate rod/cable for a remote PV array if they also feel they have very high lightning strike potential. Also see discusssions on lightning arresters. The general rule of 'one and only one ground' refers to the Earth-grounding electrode for the electrical system. This too is not necissarily "one single ground rod" as there are cases/regions where soil conditions may require more than a single rod or plate or other means to establish a suitable earth-ground. But once established, this earth-ground is then treated as a single earthing point electrically in your system, and importantly is bonded to Neutral at one (and only one) point at the first point of disconnect.
How important is grounding - yeah 'how important is your life' well said. Just know that the term 'grounding' has several meanings and is the source of much confusion. The general rule "one and only one earth-ground" is not actually quite correct when we include discussions of PV panel frame/racking earth-grounding where a separate system is also allowed.
To me, if your PV array is near-by and you don't live in Lightning-Alley use the same Earth-grounding for both the PV frames/racks as the electrical system earth-ground. That is my take on it.