The answer to that question is...quite simply because they provide a wealth of information about communities and the people within them, their customs and tastes.
In 752AD consent was obtained for burials to be made around the church. The origin of the phrase God’s acre was the enclosure of a rectangular piece of land of one acre. Early burials would norfmally have taken place south of the Church. In due course, once these spaces were used and full up, alternative land space to the north of the church was used.
In the medieval era it was usual for shrouds as opposed to coffins to be used to bury the dead. Parishes also used their communal coffin which could be wheeled to the graveside; in addition, graves would often be marked by wooden crosses until after the Reformation when stone markers became commonplace. Most graves were oriented west to east with the gravestones made from locally quarried materials. Any inscription on the gravestone usually eulogised the good deeds of the deceased.
Many churchyards contain a building which, in the era of the resurrection men, was used as watchman’s shelters; more recently they were used as a store for gravediggers' tools.
Most headstones and other memorials exist from the seventeenth century because ground would often be reused for further burials and only some families could afford any memorials. In many churchyards it is obvious that the level of the ground has risen substantially over the centuries presumably because of the number of reburials in the graves requiring more ground to be earthed up.
Development of ground used for schemes such as road-widening or even building development often meant the loss of part of the churchyard; this meant the removal of graves and headstones. In some cases the remains were exhumed and reburied elsewhere with the gravestones also transferred. Evidence exists that gravestones have been removed to help with graveyard maintenance and it is not unusual to see headstones lined against boundary walls, stacked around tree trunks or used as flags to for paving often with the inscriptions downward facing.
Today village churchyards often bear no resemblance to the churchyards of the previous centuries where fairs or pageants were held alongside village games and gambling. In some areas the churchyard was used to brew and consume beer. The church ale was sold to offset church fabric repair and maintenance.
In most churchyards the area to the north side of the church was usually unconsecrated ground and was used solely for the burial of children who had not been baptised, nonconformist dissenters and those who committed suicide.