Water Pressure in different area of Las Vegas vary from 50 psi to over 120psi depending on where the Water Authority has their pumping stations. The UniformPlumbing Code (this is the code that your local building department adopt and enforce to protect your health and safety,) section 608.2 title Excessive Water Pressure, states Where the static water pressure in the water supply piping is in excess of 80 pound per square inch an approve-type of pressure regulator proceded by an adequate strainer shall be installed and the static pressure reduced to 80psi or less. Such regulator shall control the pressure to the whole house.
Your probable wondering why at this point, Velocity cause unnecessary fiction going through your water system therefore reducing the life expectancy of your system, Most plumbing fixtures such as faucets, bath and shower valves have there volume reduce to as little as .5 gallon a minute to conserve water usage so the excess velocity undo wear on your fixtures and piping (customers often complain about pipe rattling.) and if you do have a pressure regulator they do not last forever so have it check every couple of years.
Thermo Expansion Tank
Thermo expansion is cause by heating water (your water heater). Heating water expand water, that expansion need to go somewhere during the heating process, once a pressure regulator or similar device is installed the water system becomes a closed system no where for this expansion to escape therefore a thermo expansion tank is install on cold side of your water heater for absorption of this expansion of water without it your water heater life is reduced and sometime your pressure and temperature relief valve will go off to this excess expansion.