Holding poses for a longer period of time is an extremely beneficial addition to your practice.
Holding a pose for a longer period helps build strength and stamina. For example when you hold Warrior II for a longer period, the muscles of your legs and arms have to work harder to maintain the pose.
When you hold a pose, you have time to actually feel, to adjust and to readjust. Watch out for allowing your mind to become completely occupied with this. While it’s fine to take some time to focus on your alignment don’t allow it to become your sole focus in the pose.
Holding a pose for longer then you are used to can often give space for emotions to arise. You go beyond the point that is comfortable (obviously you come out of the pose if it feels painful or does not feel ‘right’). Going beyond the comfort zone can bring up fear and other emotions.
Then there are prone poses such as Bhujangasana (Cobra Pose), Dhanurasana (Bow Pose) and Shalabhasana (Locust Pose) that even adepts do not hold for more than a minute. On the other hand, certain poses such as Sirshasana (Head Stand) and Sarvangasana (Shoulder Stand) may comfortably be held with practice for up to ten minutes. Here again, different schools of Yoga have differing views. It actually all depends upon a variety of factors including your gender, age, physical fitness, medical health, flexibility and needs.
All of the meditative poses, however, can be held for longer periods of time, without any complications. For these types of postures, it is actually beneficial to retain the asana without needing to take a break. These poses include the Easy Pose (Sukhasana), the Corpse Pose (Shavasana), and the Thunderbolt Pose (Vajrasana). Asanas are meant to strengthen the mind and spirit, while toning the body, in a safe progressive manner.