Freely printed from: https://learn.nimja.com/techniques/fractionation
Fractionation is, at its core, using repeated inductions or triggers to take someone in and out of trance as a sort of deepener.
Effectively it's many trances, over and over again.
Yes, it's that easy (at its core). There are different ways of pulling someone up and down, literally as well.
Kinesthetic or physical triggers can work exceptionally well for this. Like stroking up and down over an arm to intend 'depth'. Where stroking down from shoulder to hand puts a person into trance and stroking up would wake them. What would happen if you only stroke half-way up?
The Rehearsal Induction shows fractionation as the main technique for an induction.
There are a couple of elements at play. A lot of people do not realize that trance is happening until they feel the effects of it or they notice the contrast with their usual awareness. By doing something repeatedly, that contrast and perception of that contrast can be more vivid.
Also, after trance, most people are very susceptible to going back into trance. Repeating this, even without suggesting it, generally has the effect of making someone 'better' at going deeper.
It's also fun to realize that you do not have to wake someone up completely.
By doing something over and over again, it also lowers the threshold of expectation or nervousness for a subject. Since they're doing something they've just done, moments before.