Secondary camera is usually included in only those mobiles which are meant for video calling, because that is what the secondary camera is made for: video calling. Secondary camera is usually placed on the front side of the phone, mostly above the screen. While one performs a video chat, he or she would like to talk to the person face to face. This requires that the person has to show his 'face'.
Autofocus is a technology in cameras, both mobile cameras and digital cameras meant for photography enthusiasts which allows people to take pictures without manually adjusting the focus of the lens. Normally a camera cannot decide whether the picture it is taking is sharp or not. In the early days of digital photography, the user had to adjust the focus manually before he or she could take the picture from the device.
Mobile phones are mostly for communication. With the evolution of technology, a lot has been added to the meaning of 'communication' along with simple voice and text messages. Video sharing on the web is as common as voice for some people; people who live on the internet. They want to take a video of something funny and share it instantly on facebook or youtube.