While a pre-purchase inspection is rare, there are times that it makes sense:
You the, prospective home buyer, get the information needed to decide if a property is worth presenting a purchase agreement. This is especially useful when purchasing a foreclosed property, since the bank process can be long, unpleasant and unpredictable. A Pre-Purchase Inspections keeps you in control of the process.
Pre-Purchase inspections can be both cursory or complete. You decide. (A cursory inspection should only be done as a preview before performing a complete home inspection after under contract.