These are also known as herbal jams, the most famous of which is Chyavanaprasam (Chyawanprash.) Rasayanas (revitalizers) are most often administered in the form of Lehyams.
The reason for this is twofold. Firstly, herbs, when prepared in this manner, retain their efficacy indefinitely. Most importantly, the addition of ghee, honey and raw sugar serves to enhance and magnify the powers of these herbs. Ghee (clarified butter) is considered by Ayurveda to be one of the best of all nutritive substances. Raw honey increases Agni, the digestive fire, and, combined with ghee, speeds the herbal properties to deep and subtle tissues of the body. Raw sugar tonifies and cools the tissues.
A properly prepared Lehyam acts directly to feed Ojas, the subtle essence of the body which is the foundation of health.