As I always say, the CSV is just a simple valve, but the explanation can be complicated. With the larger CSV3A2T there is a minimum flow rate of about 5 GPM built into the CSV. With a 40/60 pressure switch and an 86 gallon size tank, you have about 22 gallons to use before the pump comes on. With that size tank and and CSV the CSV setting will be about 55 PSI. With this setting your 100 GPM pump will fill the first 15 gallons in the tank in seconds. At 55 PSI the CSV will limit the tank fill to 5 GPM, taking about 60 seconds to finish filling the tank to 60 PSI, which shuts off the pump.
When running a 2.5 GPM standard shower, the 22 gallons in the tank will last about 10 minutes before the pump comes on. With the pump on the tank is quickly filled to 55 PSI, and the CSV starts limiting flow to 5 GPM. 2.5 GPM of this is going directly to the shower. The other 2.5 GPM goes into the pressure tank for 2 minutes when the tank reaches 60 PSI and the pump is shut off. The last 2-3 minutes of your 15 minute shower will again be supplied by the tank. This means the pump only ran for about 2-3 minutes while using a 2.5 GPM shower for 15 minutes.
The tank is still almost full and the same scenario will happen again if someone waits minutes or hours before taking a shower in another part of the house or a different house. However, people tend to do many things at the same time as their neighbors. With city and community water systems they have "peak" times when everyone is home and using water, and off peak times when everyone is at school, work, or other things. So you will find that if not at exactly the same time, at least within a few minutes, someone else will use water in a different house. Your 100 GPM pump can supply as many as 40 showers all at the same time if needed. If house use for 4 houses using 300 gallons per day each is all this system is supplying, the problem is the pump is 10 times larger than needed. A 1HP would be much better for that application.
However, there is usually irrigation, pools, ponds, etc. in a system like that, which is why the larger pump is needed. If the irrigation is already running or a pond is being filled, taking a shower or three at the same time won't effect the pump in the least. Without a CSV, even with a huge tank, the irrigation needs to be matched to the output of the pump or the pump will cycle on and off. With a 100 GPM pump every zone must be 100 GPM or the pump will cycle. With a CSV the irrigation system will have constant pressure and the zones can be set to match the irrigation needs from 5 GPM to 100 GPM and the pump will not cycle. Irrigation is always most efficient when using close to or max flow of the pump. But even with zones of 30-50 GPM the amps of the pump/motor will be reduced because of the CSV, instead of running at max amps. So, it doesn't cost much extra to irrigate with varied size zones compared to always having to irrigate at the pumps max flow rate.
There is no question using a 1000 gallon tank that holds 300 gallons will cause a 100 GPM pump to use less energy than when working with a CSV and 86 gallon tank. But even with worst case scenario of only needing 300 gallons per day for 4 houses, the CSV and an 86 gallon size tank is still hard to beat. I have done the math many times and come up with 30-70 years of energy savings needed to pay off the huge pressure tank.
You will like the pressure from the CSV much better. There is no maintenance needed with a CSV and diaphragm type tank. The CSV will make the pump and everything else last longer. That, on top of the 5-10K you will save not having to replace that 1000 gallon tank will save you lots of money now and in the future. This is why pump companies classify the CSV as a "disruptive" product, do not promote its use, and try their best to talk you out of it.