What in God’s name are you talking about? The original poster is talking about slow motion, not dropping frames. You shoot a clip at 60 frames per second, and then slow the presentation of those frames down to show only 24 of them per second. So, instead of showing 60 frames in one second, it will now take two and a half seconds to show those frames because it’s only showing them at a “SLOWER” rate, hence slow motion. 24 (1 second) + 24 (1 second) + 12 (half second). You aren’t “throwing away” anything. Showing the frames at 24 frames per second is considered “cinematic” because film and theaters back in the day were shot in 24 frames per second and displayed in the theaters as such.
To the original poster, I haven’t really used After Effects, but in Adobe Premiere pro, it’s as simple as “interpreting” the 60fps footage as 24fps. You won’t lose any frames and the “smoothness” of it will depend on what kind of shutter speed you used to shoot. The slower the shutter speed, the more blurred the movement will look. I hope this helps.