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From what I can tell, this setting alters the exposure and other parameters to simulate a specific film, however why is this any better than exporting a file format that supports high dynamic range (.exr or .hdr) and then editing in post?
It would seem that using a raw file format would give you much greater flexibility.
There are a number of reasons, as @tardis-maker suggested in the other answer.
Here are a few more:
In both instances, the render of intensities is identical, but only in the latter does it resemble a "photorealistic" result because of the response of the display referred view transform. Notice how the pure primaries never desaturate / converge toward the hull established by the display referred primaries limitation, and instead carry on extending toward infinity, at their identical primaries chromaticity. While the above images show the flaws of a strictly 1D viewing transform, every colour is mangled in precisely the same way, to lessening degrees as a colour's luminance draws near achromatic. If you examine the achromatic cubes, it is clear how adjacent colours should converge to display referred white.
Related to the above point, the default sRGB output view transform captures a mere two and a bit stops of light above middle grey from a Cycles render. This is entirely unnatural when compared to our learned response of examining photographic-like reproductions, which maps anywhere from six or more stops of light above middle grey to the display / output referred transform. The above images encode approximately six and a half stops of light to the display referred view, and as such, the scene properly reflects the lighting with respect to influence of bounces and other radiometric responses without cheats or hacks to bring the result into the display referred domain.
Congruent with what @tardis-maker states above, all View transforms operate strictly on the one-way output of the viewing transform. That is, it is a means of viewing a baseline look without adversely impacting your scene referred internal values. It is entirely non-destructive in terms of evaluating an image as compared against a node chain, which corrupts and mangles values as the data flows along the chain.
It should be noted that the film emulations in Blender, although based off of solid data, are not implemented in a manner that makes them useful in the terms above. The breadth of why is beyond this post. Instead, they should be considered as nothing more than Instagram filters as a random creative dice roll.
Further viewing: https://youtu.be/vKtF2S7WEv0
Further reading: http://cinematiccolor.com http://www.oscars.org/aces/spotlight-aces-vfx Pay attention to where he discusses cheating values.
The key advantage is that it works real-time in the view-port. Of course all color manipulation could be done once the file is saved.
However having this apply to previews while you're setting up your scene means you can setup a a rough grade, and then build the lighting off of that. This allows you to get a really good idea of where you need more detail in the render, and also gives you a more accurate representation of how your lighting will look once everything is color graded.
The look settings can also help give a rough grade without much work. There's also the plus that they're based off of real life film types.
There's also a log setting. According to the manual, this is intended more as a way to trouble shoot the image, but it can also be used to get a nice flat image for use when grading.
