LT1 cooling system expansion tank

It would appear that I have ben running without an expansion tank for the last 7 years or so and my cooling system chucks out water from the header tank 15lb filler cap. It is the white triangular tank that the surge tank burps to.
Any comments or thoughts on why the LT1 needs this tank?
Thanks
Q

An expansion tank prevents the exact issue you are describing. It gives the liquid a place to go, when it expands, while allowing said liquid to return as it.cools. It is also the highest point in the cooling system, helping to bleed air from the system.
Not specific to the LT1

Hi 948, many thanks for your reply. I understand and agree with what you have said.
However, I just want to be clear.
In a 95 Corvette (where my engine was originally) there is a black tank at the top of the engine bay and another white tank lower down. I believe the black top tank is called a surge tank and the lower white one an expansion tank and they are connected to each other with a strong hose as they operate at coolant system pressure.
They operate as you say between hot and cold engine temps transferring the coolant as required.
However, in my Porsche there is no coolant transferred from the top tank to the lower except when the system has been flushed and there is still air to expel. I have found that the only time that coolant is expelled is when the top tank burps out air and carries some coolant with it. Once all the air has been expelled then the lower expansion tank neither receives nor returns any coolant.
I will continue to retain the lower tank just in case.
The above is my understanding and observation of my system but, of course, other cars and V8 swaps may react differently.
Q