Originally Posted by Double Negative
I think you might have it backwards (or I do) about the profile though; you want to convert - and not assign. That is, once you're done editing in the ProPhoto/Adobe space, *convert* it to sRGB for JPEG output (for example). If you assign instead, the colors might get a little whack.
Yes you are correct for your usage case - convert at the end of post processing for web display or printing. I normally go convert from AdobeRGB to sRGB as the last step before saving for web.
However, I was saying if you mistakenly assign the wrong profile in the scanning stage, in Photoshop, assigning a new profile doesn't change the image data. So if you normally scan in AdobeRGB and have a file tagged with that profile, and for some reason you think it would be better working with the original data in ProPhoto RGB, just assign it ProPhotoRGB. No harm done.