The sacrifices to 60fps are file size (and the resulting challenges to editing hardware, software, and output rendering), compatibility with displays and content distribution (less a factor now), negative aesthetics for some content (it's pretty far from the "film look" that is desired for some projects). And possibly a stop and a half of low light sensitivity.Okay, then what if any are the sacrifices of shooting 60fps? Less dynamic range or IQ? I'm aware of the bigger file size, but if you are cutting down to 30fps it seems there is a benefit to shoot 60fps because you have the option to slow it down a bit.
RE: aesthetics...I've already mentioned the 48fps feature release that didn't get positive response. There was "Showscan", a 60 frame, 70mm film format developed by Douglas Trumbull (2001: A Space Odyssey, Bladerunner, Brainstorm), who has argued strongly for higher frame rates than 24. He has a lot of good points. Google "great frame rate debate" for more. The short version is high frame rates result in more "reality", but that's also a negative for some content that doesn't desire "reality". The whole discussion is actually pretty interesting. Showscan failed, though for film, it may have been excellent. I saw it on a ride once, pretty amazing. And since we're now all doing digits instead of sprockets, it's a dead horse, though the frame rate debate continues.
I'm not cutting down 30fps, or any other frame rate. They all have their advantages and disadvantages. The "best" frame rate is always dictated by the final usage and intent. Yes, 60fps can be slowed easily. Many cameras will also now shoot high rates but embed a lower play rate in the metadata resulting in slow motion files without rendering. Since my days of shooting film, I've not found 1/2 speed particularly special, we more often went to 64fps or higher for display at 24, (in 16mm, and after that, or for 35mm, it took special cameras). But at least it's something.
You haven't lived until you experience a slow motion camera whipping through a load of 35mm film at 350fps! Yeah, and they did go faster...much...much faster than that.