Almost every yoga class instructs breathing alongside movement, often more insistently than it instructs the movement itself. The emphasis has both a doctrinal origin and a set of practical functions.
Breath is one of the few systems under both kinds of control
Breathing continues automatically and can also be deliberately altered, which makes it unusual among bodily processes.
That dual status is why contemplative traditions have used it so extensively, since it offers direct access to a system otherwise running without supervision.
Classical yoga treats breath regulation as a distinct limb of practice with its own techniques, separate from posture, which is why it receives independent attention.
It sets the pace of a sequence
Tying each movement to an inhalation or exhalation fixes the tempo of a class without reference to a clock.
Because breathing rate varies between people, this means each participant moves at a pace matched to their own capacity rather than to the group's.
It also prevents rushing, since a sequence performed faster than the breath allows becomes immediately obvious to the person doing it.
It functions as a gauge of effort
A posture that can be held while breathing evenly is being worked at a sustainable intensity, and one that disrupts breathing is not.
This gives participants a signal that is available continuously and does not require any external judgement about how a position looks.
Teachers use it as an instruction precisely because it converts an abstract idea about effort into something the student can detect directly.
Slow exhalation has measurable physiological effects
Breathing slowly with extended exhalation influences heart rate variability and is associated with reduced physiological arousal.
Many yoga breathing practices have exactly this structure, which is part of why classes ending with slow breathing produce a distinctive state.
The effects are real without being dramatic, and they are shared with other slow-breathing practices rather than unique to yoga.
Some practices require more caution than others
Breath retention and forceful breathing techniques are more demanding than paced breathing and are traditionally taught with supervision.
They can produce dizziness and are generally advised against for people who are pregnant or who have cardiovascular, respiratory or eye conditions.
Which practices are appropriate for an individual is a question for a qualified teacher and, where a health condition is involved, a doctor.