Covenants will set forth requirements, such as the minimum size of a house that can be built in a lot. The primary function of covenants is to provide uniformity amongst the lots/properties and help protect property values. Before signing a contract, read all applicable covenants and make sure nothing within them will cause you problems (ex: if you want to build a 1,500 sq. ft. house, you do not want to buy a lot that requires a 2,000 sq. ft. minimum home).
If you are selling property, it is a good practice to provide the Buyer with a copy of the covenants prior to signing the contract.