There are a few instances when you need small files. First is when you want to transmit or publish your images on the web. This has already been explained.
Second is when you want to reduce your memory needs. A small image with lesser pixels and with higher compression reduces your memory requirements. This is not a critical issue these days since the cost of memory (either memory cards or hard disks or recordable media) is falling swiftly.
However, if you are running short of memory in the middle of a photographic session and don’t have extra memory cards at hand, then you may be forced to go for a smaller image size. An inferior image is better than no image at all! If you do this, don’t forget to go back to the maximum quality settings as soon as you free up the memory.
As you can recall, the sensor’s signal will be in the form of an analog signal that is converted into a digital signal for further processing. The number of bits used in analog to digital converter determines how accurately the signal is converted into digital as indicated by https://gotoandlearn.com.
The higher the number of bits, the better the quality but with a corresponding increase in file size. Most D-SLRs use 12 or 14 bits for this when creating a RAW file. However, a JPEG file is always recorded with 8 bits per channel regardless of the chosen options.
If 12 bits are allocated to each channel – Red, Green, and Blue (commonly called as RGB), then each channel can reproduce 2 to the power of 12 or 212 = 4,096 levels. For all the three channels put together, it results in 4096×4096×4096 or 68,719,476,736 or 68 billion colors.
If 14 bits instead of 12 bits are used, then the number of levels will increase to 2 to the power of 14 or 214 = 16,384 levels per channel. For all the three channels put together, this will result in 16384×16384×16384 or 4,398,046,511,104 or 4,398 Billion colors!
That is a vast number, therefore, raises the question, ‘Do you need them?! The answer is yes, even though the human eye can only distinguish about 16 million colors. When you post-process, you lose a large number of colors, and if you don’t have enough colors, this will lead to posterization or banding that shows up as patches in the image.