Sometimes one neighbour objects to the use the other neighbour is making, or proposes to make to the land, or the type, size or colour of a building that is to be erected on the land, usually because:
In some situations, what the neighbour is doing or proposing to do is contrary to some private right of the adjoining owner. These rights usually arise by agreement (it may be an agreement between previous owners) in the form of easements and covenants which appear on the land title documents. For example, if there is an agreement between a number of land owners not to put up a certain type of fence (a restrictive covenant), one adjoining owner will have a private right against another. Similarly, there may be a private agreement (as there normally is between owners of terrace houses) to mutually support each other's walls (a cross easement of support). There may be an agreement which ensures open access to light and air, or which prevents building on a certain part of a block of land.
If these types of private rights are infringed, a person may go to court to seek compensation or an order to stop the offending activity.