One of the most underrated features of any consumer camcorder is its sound ability. Very good videos can easily be spoilt by the inability to hear what people are saying, or by too much background noise.
We do test this aspect of camcorders when we review them, but the tiny built-in microphones used in virtually all consumer-grade models will never provide the best results. For a start, as these are built into the camera body, they can't fail to pick up at least some of the noise made by the camcorder itself, especially if it has mechanical parts (such as a tape transport).
Positioning is also generally far from optimal. Microphones are often positioned on the top of the camcorder body with the mesh pointing upwards. So it's a miracle of modern technology that they can actually record sounds coming from the direction the lens is pointed. Some camcorders have a zoom mic facility - where the microphone attempts to concentrate on sound coming from the same place as the lens is focused. But most are essentially omnidirectional and pick up sound coming from everywhere, not just the subjects.
This is why we always mention how well each camcorder caters for attaching an external microphone. The built-in one may be good enough for quiet environments where the main source of noise is your subject matter. But it won't be very effective in most other situations. So one of the most effective upgrades you can make to your camcorder kit is an external microphone.