Any piping restriction will reduce flow rate to the fixtures (which may or may not be OK for the user) and yes that will reduce hot water consumption rate at the boiler. New low-flow fixtures shouldn't need additional restrictors inline. As long as the boiler has enough capacity to satisfy demand, additional restrictors should be unnecessary. And the point-of-use (anti-scald) mixing valves (which always have check valves) will deliver the proper temperature water, whether or not there is an upstream restrictor, as long as flow is not below the minimum flow rate of the valve.
Any piping restriction will reduce flow rate to the fixtures (which may or may not be OK for the user) and yes that will reduce hot water consumption rate at the boiler. New low-flow fixtures shouldn't need additional restrictors inline. As long as the boiler has enough capacity to satisfy demand, additional restrictors should be unnecessary. And the point-of-use (anti-scald) mixing valves (which always have check valves) will deliver the proper temperature water, whether or not there is an upstream restrictor, as long as flow is not below the minimum flow rate of the valve.