Sometimes we will inform a client that he needs a pressure reducer to which he will reply, "yea, so just close the main valve a bit and that will take care of the problem."
There is a difference between dynamic pressure and static pressure. The client would be correct if we would be seeking to reduce the dynamic pressure, the pressure that one experiences when opening the tap. However, a pressure reducer reduces the static pressure, the pressure that exists when all the taps in the home are closed. Static pressure can only be checked with an instrument called a manometer.
High pressure is deleterious to one's piping and other plumbing fixtures. It can result in multiple and constant leaking at the various pipe connections, can reduce the life of one's faucets, wears out the toilet float gaskets more frequently, wastes water, etc.
Fine, you convinced me to install a pressure reducer if my pressure is too high, but then what will happen to my shower experience?! Well, if the proper piping was installed in the house the flow rate should be fine and your shower should be alright. Also, the pressure reducer can be adjusted to suit the client's preferences.
Have a good week!