Companies that perform this certification lobbied to make it mandatory whenever selling a house. However, the certificate does not tell you the real energy consumption. The calculation is based on "weighting factors" for whatever energy production format the politicians want to favor currently, so at least where I live, in Finland - where energy consumption really matters in the winter - when you buy a house, you pay for a certificate that is not very useful, and then you ask the previous owner for the actual energy bills he had, to asses the real cost and consumption.

The latter is, of course, what everyone did already before this certificate system.

OK, it's just a few hundred euros per sale. A bigger problem in the various energy saving initiatives is that houses built to this code sometimes develop very nasty air quality problems (due to air not changing in some places fast enough, or subtle leakages in the airtight balloon where you live) which then forces costly renovations and in the worst case destroy health.