Postures, like all forms, are impermanent. ... The quest of yoga is for the formless (consciousness) ... for this reason it was necessary to organize the practice in such a way that nothing impermanent is held on to. Vinyasa yoga is a meditation on impermanence.
If asana only is practiced this might lead to excess flexibility ... in the vinyasa method, this possibility is avoided by jumping back between sides, which gives us the strength to support the amount of flexibility that is gained. ... Flexibility that cannot be supported by strength should not be aimed for. ... For this reason one needs to place the same emphasis on vinyasa as asana. (!)