The curing process has to be carefully controlled: the issue one wants to avoid above all during curing is botulism. See the entry on Curing for information about various curing methods.
Some Cured Sausages have lactic acid added to their stuffing mix, which improves safety and storage. It used to be hoped that the lactic acid would develop naturally, but now you can buy it powdered in packages. You add in very small amounts as a starting culture.
Others use nitrites and/or nitrates to guard against food poisoning.
The primary purpose of curing a sausage was to give it a long storage life, without refrigeration, especially in warmer countries such as Italy and Spain. Now, the primary purpose is the unique flavour and texture that develops.
Cured Sausages are most frequently used as a cold cut, either on an appetizer plate or in sandwiches.
Most Cured Sausages are meant to be sliced, but some are spreadable.
Shelf life varies by type of sausage.
Refrigeration can extend the storage life of Cured Sausages even further.