Let's look at some practical uses for all this. For close ups, you need a small aperture because you will need more depth of field with the large image size. If there isn't a lot of motion, a low shutter speed will help. Arrange for all the light you can get; close, fast and dim make a bad situation.
If you have a subject you need to isolate from a distracting background, using a large aperture, moving closer or zooming in to make the image larger will all serve to throw the background out of focus. You can force a larger aperture (iris) by using a faster shutter speed or a neutral density filter to limit the amount of light entering the camcorder.
In a scene where both near and far objects are important, you will need all the depth of field you can get. A small image size, a wide-angle shot if you prefer, will help. Also, more of the depth of field is behind the plane of focus than in front of it. Focus at an intermediate distance but be sure not to throw the close objects out of focus. The eye can tolerate softness in the background more than the foreground.
In any case, the better you understand optics, the more control you will have over the video that you shoot.
Night Lighting
Composition 201
Depth of Field
Vacation Videos
Camcorder Filters
Lighting: Making Video In Low Light Conditions 
Camcorder Buyer's Guide 
Tips and Tricks - Lens Filters
Directing: Directing Documentaries
Lighting: Night Lighting