As a supplement it is considered a 'pre-biotic' which will promote the growth of bacteria which aid digestion.
From www.thedietchannel.com: Inulin is a specific type of dietary fiber that is naturally found in hundreds of common foods such as leeks, artichokes, asparagus, onions, garlic, bananas, wheat, rye, and…chicory root. Do you eat chicory root? Before you answer no, you may want to take a closer look at some of your food labels. Although this hearty root is not usually eaten in its natural form, chicory root is the source used for the inulin added to processed foods.

Inulin is a natural sugar, produced by many plants and typically found in roots. On a sweetness range, it is not very sweet.