Many people in the West associate yoga exclusively with the physical postures. This aspect of the practice will be particularly helpful in helping the practitioner to find greater flexibility and strength. When yoga postures are practiced with presence and awareness, the body's general physiological systems (circulatory, digestive, nervous, etc.) will improve in their functionality. Though all of this is beneficial, the ultimate purpose of yoga postures is not to be as exercise in and of itself for a certain number of days per week, but to open up the body for meditation.
The ancient sages who developed yoga postures did so when they observed the animals stretching their bodies after waking up after sleep. They emulated these actions (as is suggested by many of the postures being named for animals) so that their bodies would be healthier and more limber for sustained periods of sitting.
Given this, and though yoga postures do provide many physical benefits in and of themselves, an ideal practice should consist of a daily commitment of at least a few minutes. This is because, ultimately, a meditation practice will grow from the posture practice and ideal spiritual practices are pursued every day. Even if it is only for ten or fifteen minutes a day, practice yoga postures after you wake up each morning so that your body will ultimately be more available for meditation should you ever choose to pursue it.