Frames Per Second

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Due to limitations of frequency divider circuits when the color standard was promulgated, the color subcarrier frequency was constructed as composite frequency assembled from small integers, in this case, 5x7x9/(8x11) MHz.[7] The horizontal line rate was reduced to approximately 15,734 lines per second (3.579545x2/455 MHz) from 15,750 lines per second, and the frame rate was reduced to about 29.970 frames per second (the horizontal line rate divided by 525 lines/frame) from 30 frames per second. These changes amounted to 0.1 percent and were readily tolerated by existing television receivers
So throughout the 2000s, the main reason you shot at 23.976 fps instead of 24P was audio post in the U.S.
Even movies shot at true 24 fps had to deal with this because a telecine transfer to NTSC for dailies and NLE post changed the frame rate to 23.976 fps, so the frame rate didn't get restored to 24 fps until the movie was finished to film and projected at 24 fps. So after a movie was edited offline, tape copies were sent to sound post for cutting and mixing sound, so they were working with material running at 23.976 fps whether or not it was shot at 24 fps or 23.976 fps