When breaking with engine, the kinetic energy of movement is converted to heat not via friction (like breaks do) but via compressing air in cylinders which does not cause extra wear on anything.
https://en.wikipedia.org/wiki/Compression_release_engine_bra...
Engine braking on a gasoline engine is actually quieter than normal operation.
http://www.jacobsvehiclesystems.com/about-us/environmental-h...