To add to the comments below, Checking an Image on screen in ProPhoto RGB is not possible, but some large gamut print processes are larger than Adobe RGB in places, so ProPhoto has its place for those. The normal workflow for printing to a high gamut device like described above is to export from Raw, which is just camera sensor data and contains no "gamut" into ProPhoto RGB, then convert to the printer profile in perceptual rendering so the gamut is not "Clipped" but this decision is image dependent. The color space is huge, but the image may not inhabit all of that space. That is why the space is used and why it is useful for this workflow.
In a high-end workflow, stick to equipment choices that support it. Adobe RGB is a large enough color space to provide bright colors, in good-quality print processes. sRGB on the other hand is smaller than most high-quality print processes and only good for internet files.
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