Admit it, there once was a time when you thought that a camera with 20 megapixels was better than one with only 16. Just me?
Admittedly, I was young teen, but I bought into the idea of pixel count. Only a few years ago, all the camera manufactures were in a megapixel war with one another. Each of them touting how they have managed to fit 7 quadzillion (not an accurate figure) pixels into a DSLR, and how the more megapixels available, the better. But is this true? And why?
In practice, a higher pixel count can capture more details, get printed to bigger sizes and be cropped down if needed. Not only that, but the sensors in these cameras are the top 'pro level' ones that produces the best colours possible.
The thought of a 36MP upwards beast is very appealing to most of us, but in reality it is overkill for 80% of photographers. The working files are huge! Which in itself puts a massive strain on our current editing systems if we're editing a wedding or an event, or even a shoot which has 1,000 photos to go through. Secondly, the bigger the sensor, the more any shake becomes visible. It makes a good tripod and photographic technique an absolute necessity.
Fine details that get captured are unbelievable however. For landscape photographers, a large pixel count is a godsend. Portrait photographers see this as a double edged sword. The details captured are amazing, but it also means they get alot of details in blemishes. This means more time cleaning up and softening skin in photoshop.
Most photographers can get away with a 12MP camera for 90% of shooting, provided there isn't much in the way of cropping. I regularly shoot with a 12MP Nikon D700 without issue, and this is my go to camera for weddings. I will still shoot landscapes with it, but I would like a 36MP D800 for the fine details.
In conclusion, the pixel count should depend on what you need. If you don't need a huge pixel count, then there is no reason to get a camera with it. These days though, most cameras have megapixels enough for every application. Save your money and buy a better lens.