Alright, enough with the Apple stuff. Let's talk photo!
There was a time where the best pro DSLRs had a CCD sensor capturing images of few megapixels (the Nikon D1, for instance, was 2.7MP). That's 4x less than the front-facing camera of some smartphones (like the HTC Desire Eye). And, for a while, there's was a megapixels war between camera maker where they all tried to make the highest resolution sensor possible. Today, you can buy the full-frame Nikon D810 that is equipped with a 36.3MP CMOS sensor.
What gave me the idea for this blog today was when I read that Sony and Canon are expected to announced a camera that's around 50MP (!). That's a lot. Now, I personally have some problems with those high megapixels camera (if they are full-frame or less).
First, more pixels makes each pixel smaller, thus reducing the quantity of light that each of them is exposed to. If there is less light to each of them, the low-light performance of the body is reduced, resulting in higher noise level which makes you image less sharp, more muddy and strips some data from it. Not cool.
Secondly, the file size is bigger. My little 16MP Sony a57 outputs file that are about 16MB (they are 12 bits). If you go to a 50MP body with a 14 bits per pixel, the file may be more around 60MB. That means you need to have more SD cards or buy some that are higher capacity or always transfer the pictures into your computer, thus losing time and getting annoyed. Also, your computer will be slower with them (because it needs more resources to handle them), making you need a faster one or dig through your patience.
Thirdly, 50MP is too much is almost all cases. Most monitors and TVs today are 1080p. That's 2MP, so there is 48MP you can't even see. If you have the new iMac with Retina 5K display, you are sitting behind a 14.7MP display. That's almost 4 times less than the 50MP image. Also, if you want to upload to a website, you'll want to resize them to a smaller size so they load quicker.
However, having more resolution for products and still life is very nice. But, if all you zoom in is noise and garbage, what's the point? I think it's worth to mention that the size of the pixel is not the only factor determining the noisiness of your image and that the image processor inside the camera can go a long way toward helping that. Still, having more small squares inside your camera is not helping.
And, for portraits, isn't going backward to have more megapixels to play with? Because you can see every pores or flaws is your model's skin.
The only place I see high MP being useful are with images for ads that you'll print very big (like a billboard, an ad like those in the airports or the images they often put on the building when they are being built). For that, however, there are medium-format cameras.