Ucchistha Chandalini is the "outcaste" Devi who governs the remainders or left overs in a puja or sadhana. As Matangi, the energy is also associated with magnetizing principles and non-divisive wisdom. Mantangi as a particular all red form is also known as Sumukhi Devi, and is described as being seated on a corpse holding a kapal and sword. It is said that sadhaks who perfect the Vidya of Ucchitha Chandalini need not worry over errors of commission or omission in their sadhanas, as even "errors" would be seen as remainders and thus offerings. Indeed, while it is easy to conceive of remainders/left overs in terms of an external puja (via the various articles of worship), the Vidya is most profound in its interactions with the inner qualities of a sadhak. In our sadhana, we are likely to have left over aspirations that we've been unable to properly channel, energies that we've not be able to assimilate properly, or lingering elements of all sort, and including a practice of Ucchishta Chandalini brings everything into balance and perfection (imperfection as perfection). Also in our sadhana, we are likely to make some errors, maybe some of our mantras are not correct (or we missed the proper amount), or our concentration isn't sharp, or our compassionate intent isn't as expansive as it should be, but in these cases (and others) Sumukhi Devi excepts these "mistakes" as offerings. Inherent in this Devi is a deep understanding of unitive wisdom (one taste), which is the true siddhi that the sadhak needs to abide as. So one shouldn't just understand this Vidya as "offering the remainder to the Divine to make it Divine", but should come to the unitive understanding of everything as Divine expression. In this way, like in other areas of Tantra, we unite in/as the Deity and operate from their/that perspective. Ucchista Chandalini functions in the subtle centers and the various yogic processes which accompany sadhana, so "remainders" or "left overs" also refers to energies in our subtle channels. Therefore, the wisdom of the Devi is also functional in our subtle experience. Uccishtha Devatas of all sort are said to be quick to respond, and many of their sadhana requirements are more easy to accomplish than other deities. As one gains experience in the Vidya, then it begins to permeate one's day to day life. For those interested in benefiting others, it can be an important Vidya both in terms of how one's own expression is "received" and also in clearing obstructions in others. If in a moment we are conventionally unskillful in a daily interaction, the knowledge of the Vidya can make it skillful none the less (it will somehow take the edge/remainder off and communicate something positive.) One may think that as one gains wisdom, that one will work with Ucchishta Devatas less (as presumably there are less energetic remainders), but at a certain levels of understanding, one views all manifest existence as a remainder of sort, and certainly one's own life (via interaction with the world) can be seen as such.