Here is a diagram showing the relative size of sensors. There are more sizes than this but let me say that this shows the glaring difference between the three most commonly owned cameras, namely, the full frame DSLR or Mirrorless, the APS-C DSLR or Mirrorless, and the point and shoot/bridge camera.
This is why as a developing amateur, I recommend the ASP-C size sensor. Now professional photographers don't get up in arms! I will readily admit that if one is planning on earning a living shooting photos he or she should have a full frame camera. I know that a lot of pro's have an APS-C camera as an emergency back up, but the pro will do better with a full frame. However, there are some really great images made with APS-C sensor cameras and that is exclusively what I shoot. What you get with an APS-C sensor is detail in the foreground, middle, and background. Also, when it comes to shooting portraits, you get super great detail up front. There is greater detail in the eyes, skin, lips, hair etc.
It infuriates me to see someone who has deep enough pockets purchase a full frame camera, but not enough skill to make their photos look any better than a P&S camera. I am on a lot of Facebook groups and believe me, I see photos every day that are shot with expensive full frame cameras that are barely in focus, dull and look like they were shot with the smallest of sensors. Maybe I am just jealous but it still makes me angry :).
Now then, small sensors do have their place. They make it possible to zoom to great distances with a fairly small camera and relatively short lens. An example of this camera is the one bridge camera that I have kept around. It is the Canon SX40 HS. If you look at the photo of my Sony A3000 at the top of this post you will see that it has a very long lens. Further, it's maximum zoom is 215mm (larger with the crop factor but that is another blog article). The Canon pictured to the left has a zoom capability of 840mm. Yes, you read me right, 820mm zoom. It allows some spectacular moon shots with a very small sensor. It has a fixed zoom lens but it allows a range of 24mm to 840mm (in 35mm equivalent terms). Here is a moon shot I took with it.
This was on a tripod, 100 ISO, f/8
This is just scratching the surface of the importance of sensor size but will be sufficient for today. Hopefully I have given you food for thought and you will not waste as much money on P&S cameras as I did. One thing is certain. You can get a lot of really nice images with an APS-C sensor on either a DSLR or a Mirrorless camera.