The men and women who operate public water systems do an amazing job of ensuring all public health standards are met at all times. But no system is perfect- equipment can fail or temporarily malfunction, and we humans are not perfect- so mistakes can happen and sometimes there is a chance of some less-than-perfect water slipping by and getting into our water supply. Plus there are contaminants in our water that are not regulated, or only tested for every few years. Or byproducts of the disinfection process that have not been fully studied as to the long term effects of drinking water with those byproducts in them.
We have always advised people to remove the chlorine and/or chloramines from their water once it enters the house. The purpose of these is to ensure that the water that leaves the treatment plant arrives at your home safe to drink, should there be a compromise in the delivery system somewhere along the way to your house. Once it has arrived at your house, there is no further need for the disinfection residual, assuming your plumbing meets appropriate codes (proper backflow prevention, no cross connections, proper air gaps and so on). This is typically done whole house, as the water enters from the street.
For drinking water, our industry has always considered reverse osmosis to be the “Final Barrier” to removing a large percentage of just about everything in the water. This is typically a Point of Use system, specifically for drinking, cooking and ice making. There is generally no need for whole house systems on a public water supply.