Encoding all video at high frame rate is often just a waste of resources, and you can get higher quality video at lower frame rate in many cases.
This is because you have three variables:
- Bit Rate -- how many 1's and 0's you will produce in one second
- Resolution -- how many pixels there are in each frame
- Frame Rate -- how many frames there are in one second
- 15 fps -- Talking Head Video, such as interviews, seminars, etc. especially when the camera is on a tripod
- 25 fps -- Good all around setting. Note that this is the standard for television in Europe (PAL)
- 29.97 or 30 fps -- Use for sports and other high motion video.