Most good 24bit recorders cannot achieve more than a 20bit or so noise floor thanks to the limitations of analog components. With the best equipment you can get a noise floor about 30-32dB lower than the limitations of 16 bit. That is theoretically 30dB of free digital gain! If the end format is a CD, that is.
Most ambient noise levels are also above a 16bit noise floor, so in real use, there isn't much benefit to anything higher. Still, it is good practice to record in 24bit and give yourself some headroom to work with, but not too much, mind you
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I record in 48kHz 98% of the time since a lot of my recordings are accompanied with video, and I'm too lazy to switch sample rates the rest of the time. Like drewfx1 said, a higher sample rate with allow you to record higher frequencies, full stop. There is no other practical use during recording....seriously. All else is fiction, speculation, and conjecture. On a side note, the distortion of most microphones increase exponentially once you pass 20kHz, even ones designed to reach 30 or 40kHz. And if you feed that to a speaker system designed for 20kHz playback, you may also increase the distortion throughout the entire range of the tweeter. All bad things!!! so I would recommend using the maximum sample rate for the needs of the material you are recording.