Fibre supplements are a relatively small part of the market, with each supplement having no benefit over and above that which can be gained from consuming sufficient amounts of the fibre itself within foods. In fact, foods which provide larger amounts of fibre are inherently health-promoting due to the additional nutrients that they provide and as such a fibre supplement should never be considered to be a 1-1 replacement for a typical intake of dietary fibre.
With that said, soluble fibre supplementation has been shown to be effective in the management of diabetes, and psyllium husk supplementation appears effective at reducing symptoms of metabolic syndrome. These effects are likely to simply be functions of the fibres themselves and therefore a food source would have been preferable, but it’s still the case that a fibre supplement could be a temporary solution for those not consuming a large amount of fibre for any amount of time, for any reason.
As you can see from the above, food supplements generally fall within a few small groups and serve a single purpose – to allow you to consume a normal amount of a nutrient to avoid the negative consequences of not doing so. These should not be considered compounds that have positive effects, but rather to be products which enable you to avoid negative ones. The next category, however, can indeed be viewed as products designed to improve some aspect of health and/or sports performance over and above that which would be expected from a given individual who had otherwise optimised their diet, lifestyle and exercise programming.