I did a CGI course at uni and we were told about the wonders of Cinestyle when filming. Of course ever since then I've been using it for both filming and photos on my own camera, but a friend who is a photographer recently said she doesn't understand why I destroy the contrast since RAW captures enough data anyway (and I realised that was a pretty good point).
Could it be useful if I use Cinestyle for RAW photos, or is it a bit pointless?
For most (maybe all) manufacturers/cameras, the picture styles are not applied to raw images and so it just doesn't matter. It may (also dependent on camera/software/software version) change the way the postprocessing is done if the raw metadata tells the software about the picture style used and the software cares about that, but technically it does not change the raw data. Besides this, the raw data is the raw data and for canon cameras the only adjustments that actually changes the data saved to raw (besides exposure parameters) are the sraw modes, and these only change resolution, and the dark frame subtraction, as @MichaelClark reminded me in the comments (some cameras may have additional features affecting raw data, but picture styles is usually not among them).
For video work, it makes sense to apply reasonable picture styles since usually the wider dynamic range of the camera with a linear response curve has to be squeezed into the lower dynamic range (resp. value range, e.g. 8 bits) of the file format and usefully distributed among them.
