The chewing that chaffs encourage stimulates the production of saliva which protects the upper stomach from acid in the lower stomach and thus helps to maintain gastric health. So to answer your question yes feeding a chaff is a very useful addition to the diet.

Can you feed too much chaff?

This can lead to serious problems, from hindgut acidosis to ulcers to colic. By adding chaff in with concentrates, and wetting it down to keep it well mixed, you force your horse to chew more thoroughly and slowly. This can mean your horse takes 45 minutes over his grain meal rather than just 10.

Why is chaff bad for horses?

Chaff and Digestion

Chaff will also encourage chewing, prolonging feeding time and the production of increased amounts of acid-buffering saliva. ... Feeding chaff will slow down the horse's intake by encouraging chewing, helping the horse to digest the feed properly.