I work in the film/TV industry and we still try to use Quicktime 7 Pro over Quicktime X. Here's why:
You can't quickly, like with hot keys, mark the in and out or toggle the play range from full to in/out and back.
You can't view the timecode while playing. You can't have it show frame numbers instead and show them while playing.
You can't play certain formats (like DNxHD) natively forcing you to wait through a time consuming conversion before even knowing it it's the right movie.
You can't access the properties to correct for aspect ratio issues.
You can't export to any of the wide variety of codecs available easily (not even the various flavors of ProRes).
Neither application allows for viewer color space conversion (like from Cineon to rec.709 or sRGB) or to account for atom Gamma bits or other under the hood color modifications for display. But on the other hand very few alternatives allow for multiple windows to be open at the same time so it continues to be the goto for us.
The loss of QuickTime 7 Pro has been devastating to the film and TV industry and nothing has really risen to replace it, especially not QuickTime X.
Dan