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Hi Eyeayen,
Fixed focal length or "prime" lenses as they are sometimes referred to, on the whole offer superior image quality over a zoom lens, as the optics don't have to cater and correct for both telephoto and wide angle shots. They are generally used for specific purposes, like motorsports and wildlife (200 to 500mm), portraiture (50 to 105mm) and landscapes (18mm and below), depending on the focal length.
Framing the shot is done with the feet as you mention and photographers have to pre-position themselves when shooting things like motorsports. Similarly with wildlife shots. The photographer either sits in a fixed position and waits for the animals to appear in a location that they are known to frequent or will have to stealthily track the animal from a distance.
Primes also tend to be "faster" than zoom lenses too, with the majority of telephoto lenses having a maximum aperture of f/2.8 or f/4. 50mm and below lenses often go down as far as f/1.4 and even f/1.2 on occasions.
Incidentally, one of the best lenses you can own is a 50mm prime for close portraiture and as a general walk about lens. My Nikkor 50mm f/1.8 is probably my favorite lens and it was also the cheapest at £109!
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