Salt provides three important attributes to food: flavour,
preservation and functionality.
Today, salt is most commonly used to season food - sometimes for
its own flavour (as in salty crisps), but more often as a flavour
enhancer.
Salt can also be used as a preservative. By lowering water
activity in food, salt limits microbial growth, acting as a
preservative in salt cured fish and meat products and playing an
important role in cheese production.
Salt's water retention and structure properties are also
important in food production. By retaining water in meat-based
products, salt makes sausages appear plumper. And by providing a
structure, the crystal lattice of salt helps bread maintain its
volume.
Finally - and this is a more recent application - salt is used
as a textural enhancer. The humble salt crystal has come to signify
culinary flair and decadence - but like any kind of decadence
needs to be treated with moderation in order to stay healthy!