Over time your heating system can develop a build up of sludge within the pipes and radiators, which in turn restricts the flow of water, making your boiler work harder to push the water around. At the same time your radiators may develop cold spots, for instance, despite bleeding the radiator the bottom part at the middle never fully heats up.
If that is the case you may well benefit from having your central heating system flushed out, to remove dirt and debris and make the heating more efficient.