This article on full frame sensors is going to focus on the pluses and minuses of choosing a camera with a full sized sensor.
The definition of a full size camera sensor is simple.It's the same size as a 35mm camera's film size(24mm by 36mm). Before digital photography arrived, all of the 35mm film was of one size, full.
Now with digital photography, there are many options for size, regarding the sensor which has replaced film. There are also considerations about pixel density.
Full frame sensors are good for landscape and architectural photography where small details are very important. You get great image quality and you get the full usefulness of wide-angle lenses.
Compact cameras with smaller sensors don't give you as much background blur in portraits, because they give you a deep depth of field at the same aperture. Small sensored cameras are great for snapshots. They come in small cameras and are very easy to carry.
Image quality goes way up with larger sensors.
Large sensors have much less "digital noise" in low light situations.
One of the disadvantages of this larger size is that your lens and camera must be bigger too.
This means heavier and more expensive.
Larger sensors are more expensive to make and therefore are more expensive to buy.
Larger sensors give you larger digital files that take longer to process and require more memory, (although memory has gotten very cheap).
When you want a deep depth of field, you have to close down the aperture quite a bit.
For a given number of pixels, the larger sensor allows for larger pixels that provide wider dynamic range and lower noise. Essentially that means a large size will give you a better quality on several fronts.
One of the photography terms that is associated with sensor is crop factor
If a sensor is full-size the focal length of a lens is the same as the lens would be on a 35mm camera. As you can see from the chart below, if your lens was a 105mm lens and you had a camera with an undersized sensor that has a crop factor of 1.6, then essentially that same lens will be like having a 168mm lens.
Smaller sized ones offer some advantages for telephoto photography because the smaller angle of view of small-sensor DSLRs enhances the telephoto effect of the lenses.
For a more detailed explanation of Crop Factor and an illustration of it, read this article: Crop Factor
Here are the four sensor sizes and the resulting "square mm areas:
Four Thirds sensor is 17.3 mm x 13mm = 224.9
APS-C = 23.5mm x 15.7mm = 368.95
APS-H = 28.1mm x 18.7mm = 525.47
Full-Frame = 36 x 24 = 864
You can see by the areas that a full frame sensor is more than 3 times as big as a Four-Thirds sensor and more than twice as big as an APS-C sensor.
Another important impact of different sensor sizes is the impact on depth of field. Cell phone cameras and small point and shoot cameras with smaller-sized sensors have a very large Depth of Field.
Full-sized sensors have less depth of field which is great for portrait photography.