It is to see if reducing and non reducing sugars are present.
a reducing sugar is one which
can donate electrons and includes all monosaccharides and some disaccharides
An alkaline solution of blue copper (II) sulphate is added to the sugar and subsequently heated, in the presence of reducing sugar, a red precipitate of copper (I) oxide is
formed.
In the absence of reducing sugar, the Benedict’s reagent does not change colour
