Wych Cults are similar to the Kabals of the Dark Eldar, in that they originated from the Pleasure Cults of the pre-Fall Eldar. While Kabals evolved to be a collective of Dark Eldar claiming territory and cooperating with each other to collect souls and thus stave off death, Wych Cults evolved to further their skills in combat.
A Wych Cult member is obsessed with honing their skills in hand to hand combat, and once they are sufficiently competent with Wych Weapons, they may choose to train in the use of Hellion Skyboards and Reaver Jetbikes. The fighters of a Cult train constantly with each other, and they are expected to kill their opponents if possible. In this way, the weakest members are very quickly weeded out, producing only the best warriors with which to represent the Cult.
Wych Cults don't usually have large enough numbers to perform their own raids, so they work as mercenaries for Kabals, lending them their strength in exchange for slaves, the currency of Commorragh. The coliseum puts on fights regularly as an exhibition of their talents, pitting Wyches against each other as well as groups of slaves, or even fearsome alien beasts collected during raids. In this way, they are able to advertise their skills to Kabals, and bring in more work.