The sum of all key rate '01s is equal to the change in price from shifting the yield to maturity by 1 basis point.

The key rate shift of the 10-year par rate leads to higher spot rates for all maturities.

By choosing the key rates for the US Treasury as 2-, 5-, 10-, and 30-year par yields, a 15-year on-the-run US Treasury bond has no exposure to the 30-year key rate shift.