“Mindfulness of breathing (ānāpānasati) is a complete meditation practice in itself. It is complete from the beginning to the end – even up to the path-fruition (magga-phala), that is Nibbāna. Because of this completeness, its aim is different from other meditation objects (kammaṭṭhāna). This practice has breathing in and breathing out as its only object. Thus, there is nothing that has to be moved, changed or set up. The breathing is always present.
Mindfulness of breathing is an extremely convenient method of practice for, as indicated above, there is no need for external objects to carry around or set up. Whenever one decides to practice, he or she will find the in- and out-breathing there. This is not the case with many of the other kinds of meditation objects which depend upon external objects such as colored discs, corpses and so on. Rather, by taking the in- and out-breathing as a meditation object, one takes his meditation object wherever he or she goes, since the in- and out-breathing always accompanies the meditator. Thus, it is rightly said that the practice of ānāpānasati is convenient.
Another noteworthy feature of the practice of mindfulness of breathing is that it is harmless. It is an extremely refined meditation object that doesn’t lead to fear, excitement, commotion or confusion...”