No. You don’t NEED it. But if you are planning on doing mainly free camping/national park camping without 240 volt power then this system gives you piece of mind as it tells you exactly how much power you have left in hours if you continue doing exactly what you are doing at that point in time.
So if you are running a fridge and have a laptop plugged in it might for example say 4 hours. But then you plug in your solar blanket and it recalculates to 8 hours. Then your laptop battery is full and you unplug the charger and the system recalculates to 12 hours.
There are also other more simple options such as volt readers that you can plug into a 12 volt outlet and will tell you how many volts are left in your leisure battery.