Like everything in life, the better something is prepared the more likely the outcome be better as well.
At Art-Tech we recommend all subfloors to be refastened, sanded and clean of any debries prior to installation. More so accurate moisture testing and temprature is always completed to make sure site is safe for hardwood installation. The hardwood shoudl be acclimatized to the site prior to install unless moisture reading confirm competability.
At times the current subfloor might be in diere condition or simply not thick or strong enough to support properly the new flooring ans so addtional underlay needs to be isntalled to make sure a long lasting flooring is properly installed.