You piggies need to listen, things get technical here and I'm not gonna repeat myself.
You know how steam is water vapour or water that has changed state from a liquid to a gas? Water changes to a gas if we raise it's temperature to beyond water's intrinsic boiling temperature which is around 100℃. Water vapour takes up more space than water because the molecules are excited and bounce around like a millennial with ADD at a coffee tasting and so take up more space, or at least that's what they taught us at school before the quantum physicists started scheming up some left field shit that no-one understands and completely disproved the atomic theory of matter. I want my 3 years in standard 6 back damnit!
Anyway, same thing applies to gas but in reverse. If we want to store gas compactly, it makes sense for us to store it as a liquid rather than a gas because we can store more of the good stuff in the same amount of space. 270 times more!
So clearly we want to store gas in a bottle in liquid form. The obvious way to do this is to reduce it's temperature to below it's boiling point - which is around -40℃ for LPG - picnic weather in Siberia, but a little chilly for the rest of us.
Another way to beat a gas into a liquid is to pressurise the tank we are decanting it into. My girly looking Irish mate Robert Boyle proved that if we ignore irritating things like reality we can assert outlandish stuff. Specifically Boyle proved that PV=k, which basically translates into - there is a relationship between the temperature, pressure and volume of a gas. Any change in any of these 3 variables will have an impact on the other 2. So if we pump the pressure up either the temperature must drop or the volume must increase or both.
And that's exactly what we do when filling a gas bottle. We force the gas into a cylinder under 12 bar of pressure, this causes the temperature of the bottle to drop a little, but more importantly for my epic story I am telling here, it forces the gas to change state from gassy stuff to watery stuff allowing us to store it as a liquid in the bottle. That's why if you shake a gas bottle it feels like there is water inside. (unless you bought the bottle on the side of the road from a dodgy rogue dealer who lives in his bakkie with his gas bottles and his goat, then that actually is water in the bottle)
What's any of this got to do with gas regulators? I'm getting there.
With our heavily pressurised bottle filled with liquid gas (LPG get it?) we have an insanely effective transportable energy source. When we pull the gas out of the bottle, it expands 270 times from the liquid it is in into a gaseous state, and that vapour then mixes with oxygen to form a combustible fuel. That's why you can run a stove for such a long time on such a small gas bottle.
While the gas is in the bottle, it's going to have an insatiable desire to change from a liquid to a gas (remember it's boiling point is a peachy -40℃), but because the pressure is so high, it has to tow the line and remain in liquid state - it's LPG's equivalent of feeling like a rat in a cage. A corollary to this is that the bottle will maintain it's pressure until there is no more liquid in the bottle. That's why LPG (or one of it's constituents) is used in pressurising aerosol cans, and that's why you can chase your siblings around the house with a can of DOOM and a lighter for hours of arsonal fun. (There is no evidence it's effective in the banishment of demons though). It's also why gas pressure gauges help you nada in trying to determine how full your bottle is. The bottle's pressure doesn't drop until the liquid gas is finished, so the gauge will notify you around the same time your stove stops working.
Because the bottle maintains it's pressure till there is no more liquid, and because that pressure is high (relative to the pressure of working in government) we can do clever stuff. In order to get a flame to burn and generate heat, we don't need anywhere near bottle pressure. we can work with small fractions of bottle pressure. While not directly correlated, there is a relationship between pressure and flow rate (volume) and for our purposes, dropping the working pressure also reduces the consumption. So nearly all domestic LPG equipment run on a standardised lower pressure supply affectionately know in the industry as "Low Pressure". Even high calorific equipment like water heaters operate on low pressure supply.
As a wise man whose identity is sadly lost to the winds of time once said, the best thing about standards is that there are so many to choose from. Unfortunately, while this is cynical, sarky and definitely true, you're going to find you still need 'em. (unless you're French, then you do shit your way and nobody understands how it is supposed to work)
Gas, or more accurately Liquified petroleum gas (LPG) is standardised in South Africa on 2.8Kpa as the "Low Pressure" standard, and almost all domestic equipment in use operates at this pressure. Bottle pressure is around 700Kpa to 1000Kpa (depends on ambient temperature) and operating pressure is around 2.8Kpa, so clearly we need to reduce the pressure coming out the bottle before we deliver it to the appliance. And the thing we use to drop the bottle pressure down to operating low pressure is... A gas regulator(it does for gas what cocaine does for air traffic controllers)
So there you go, a gas pressure regulator is a thing that drops the pressure of your gas line from bottle pressure (1000Kpa) to low pressure (2.8Kpa) so that you home gas appliances are operating on the correct standardised pressure. It has both safety and consumption benefits and basically no downsides. It looks a little like a UFO stuck against it's passengers will in situ by some unknown alien force only the French stand any chance of understanding.
How does a regulator drop the pressure? Mostly magic, but that's a discussion for another day.