Economic and social historians have been wary of using the extents attached to inquisitions post mortems as historical evidence. Those produced before the Black Death were alluring because they offered in abbreviated form manorial surveys with indications of the size of demesnes, numbers of tenants of different status (free, customary, cottars), rents and services, and assets such as woods, parks, fishponds and mills, all with annual values attached. A fortunate researcher, especially one working on the early years of the fourteenth century, might occasionally be told in the extents about the fields in which the demesne lay, and the system of crop rotation in use, together with the names of the tenants and the size of each holding. There might be a list of assarts, or details of urban property.

The extents attached to IPMs were welcome to economic historians because they contained information about the estates of lay lords whose own administration did not produce many documents, or alternatively for which any archives that once existed had been lost through family discontinuities. They were especially useful for investigating the landed assets of minor lay lords, the gentry, which one suspects were administered orally when the knight, esquire or lesser lord was in residence, leaving very little written material in the family's own collection of documents. An invaluable feature of these records was their survival in the state archives for parts of the country otherwise lacking in abundant local evidence, such as the woodlands of the midlands, in Staffordshire for example, or in the Welsh border counties of Herefordshire and Shropshire.