We are all hindered by unintended consequences, Sweden one might argue a global leader for harvesting leftover heat was hamstrung by the law which prevented other suppliers accessing the district heating grid, but that changed when a law was passed last year that allows outside suppliers to deliver heat through the district heating grid. Now the town of Kiruna in northern Sweden can use waste heat from their local industry to cheaply heat homes, a neat solution when the mercury hits -30 Deg C in winter. Details are scarce in the Guardian article  however using waste heat whether from industry or power generation is cost-effective when the distance (where increasing distance equates causing increasing heat loss) between the source and end-user is not great.
Less commonly known is that waste heat can be used in the tropics to drive air conditioning, necessary in large parts of Asia. Low grade heat energy is often dumped into rivers or the sea, instead it can be used to change the concentration of liquid salt, e.g. lithium bromide, creating cold water for comfort cooling.