Comment by Klaus23
Your point is valid, but that's not really what we were talking about.
You said that using data centre heat is an alternative to reversible computing. This is not the case. Neglecting efficiency improvements and instead moving the data centre to a place where the heat can be used is worse than making it more efficient and using heat pumps with the saved energy at a much higher efficiency. It is even worse if the heat is dumped into the air, as istjohn said.
Also using the heat to heat homes would be even better. The two concepts aren't mutually exclusive.
How exactly is using what is essentially free energy worse than using heatpumps? You will build datacenters anyway; it _will_ happen, irrespective of using or not using heatpumps. Using 10Mw of energy from a DS would mean that you'd need 2.5Mw less of energy for heatpumping.