Pipe insulation should be used where ever possible. Covering the heating pipes with insulation means that less heat is wasted and so the radiators will be warmer as heat is not lost under floors etc. Cold water pipes should also be insulated, especially in lofts where there is loft insulation as less heat goes into the loft and so the pipes and tanks etc. are more likely to be effected by the cold weather.
Fitting pipe insulation is often just a simple case of sliding the insulation over the pipe and then fixing the insulation in place using some cable ties or tape. Here this insulation is covering the condensate pipe from a modern condensing boiler.