SMART phones makers seem to have followed the lead of Gillette razors. But instead of blades, we now have cameras.
In terms of possible performance gains, a dual-camera system isn’t just a gimmick. If done right, a pair of sensors and lenses working in tandem can address some key limitations of a smartphone camera. For traditional photography, it can simulate using an optical zoom lens and replicate the benefits of using a larger sensor. Doubling up on cameras can also pave the way for better augmented reality and fancy post-capture tricks.
A Larger Sensor Area
The biggest shortcoming smartphones have in comparison to DSLRs and high-end compact cameras is sensor size. Phone sensors are small—about 1/20th the surface area of a consumer DSLR’s APS-C sensor—and a big sensor almost always means better image quality.
There are a lot of variables, such as pixel density and the image-processing pipeline and the quality of the lens you’re using. But to oversimplify things: A bigger sensor has bigger, smarter photosites. Big photosites perform much better in the dark, capture more detail, and collect more data at the pixel level.

So by using two smaller sensors, smartphone cameras can simulate the effects of having bigger sensors. That’s important, because putting a large sensor in a phone presents challenges in terms of thickness, lens size, and thermal management.
Packing two sensors gives a phone twice the surface area for collecting information and gathering light. That should translate to better low-light images, wider dynamic range, better HDR—in theory, at least. A dual-sensor setup can also improve the speed and accuracy of the autofocus system.

Optical Zoom With Fixed Lens(es)
Unless you have a lens attachment, the best way to zoom with a smartphone camera is to physically move closer to the subject. You can use digital zoom, which is basically the same thing as enlarging an image after you take it; your image resolution takes a hit. Optical zoom is better. It magnifies faraway subjects with the lens, preserving details in the process.
But serious optical reach takes up space, and nobody wants a moving, protruding lens built into their phone. A dual-camera setup could be the best way to build optical zoom into a mobile device: One wider-angle lens that most smartphone shooters are accustomed to, and a telephoto lens that helps bring in that skyline.

Refocusing and Other Fun Tricks
The sensor technology is different but using a pair of lenses and sensors can help replicate the post-capture refocusing features of the first lytro cameras. Refocusing after a photo is captured is one of LinX’s marquee tricks.
That’s not the only fancy feature a dual-camera setup could bring to the table. Things like instant cinemagraphs and 3-D effects could benefit from two lenses and sensors capturing information at the same time.

Depth-Sensing Skills
A two-camera setup can also go beyond photography applications. It’ll let your phone gauge the distance between itself and real-world objects, as well as the size of those objects. It can also help create 3-D models of things by examining them from different angles and focal lengths at the same time.

Imagine having dual cameras like an Aero plane with two pilots onboard, both combining well to perform an important role. One day, we'll probably look back and remember when phones only had two main cameras.

Why rather not have a phone with dual camera?

One camera never do us finish na two again.

Phythondancer:
One camera never do us finish na two again.

No mind am

Phythondancer:
One camera never do us finish na two again.

Bokeh like effects can also be created on a single camera just like the Canon X

Ennyholar:
Bokeh like effects can also be created on a single camera just like the Canon X

true, but imagine that on two in one device.