Having the ability to come and go from the Desolate Cold Stream as one pleases is a trump card.
With this, the Desolate Cold Stream becomes their source of troops and a training ground, capable of continuously delivering battle strength of various levels.
In fact,
Lu Qingfeng had already entertained this idea upon learning about the situation in the Desolate Cold Stream. At the time, however, he was unaware of the Six-winged and the Northern Cold Snowy Domain's grievances; he merely thought of selecting top True Immortals from the Desolate Cold Stream, either to place them in Lingnan on retainer or to send them to serve in the General Mansion of Capturing God.
These True Immortals, trapped in the Desolate Cold Stream, are incapable of escape despite all their efforts.
With this as a temptation, getting them to serve permanently might not be an issue, and if they were simply to serve for a set number of years in exchange for their freedom, it's likely none would refuse.
