I prefer to manually set and adjust the light/power output of my flash units. In static portrait situations, where the distance between the subject and the lights doesn’t change much, I get very consistent flash exposures and color from shot to shot. TTL is great for fast-paced photography (i.e. event photography) but I prefer manual control if there’s time to take a few test shots as I dial-in each light to achieve the effect I want. And once the power settings on those lights are set, I can be confident that a series of looks and poses will turn out well.
Setting up Manual remote flash triggering using an external flash trigger: