What it would do is let people know the exact historical selling prices of properties in a particular area. It would remove the need to rely on the rediculous auction price 'sold for in the region of x million euro' reports in newspapers which is as close to the truth as you can get in this country at present.
During the boom times auctioneers tended to base their asking price on whatever the last similar house in the area they sold for plus a markup. As final sale agreed figures tended to exceed the asking by anything up to 10% we have nothing to rely on but surveys from vested interests like the IAVI and asking price reports from Daft which do not reflect the market clearing price as asking prices are aspirational at best.
This is all hypothetical at present.
As long as FF are in government they will never allow such a system to be set up. It goes against the desires of their friends and benefactors in the construction industry.