It's a helpful addition, considering that not many desktop video players offer a similar feature.
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Another change is that the HQ/HD flag is now sticky. Once you click on HQ or HD, YouTube will save the setting in a cookie and all the other videos will use the options, assuming that they have high-quality versions. "When you switch to view a video in high quality and lean back to enjoy the wide player experience, having to lean forward again to switch the experience back on, video after video, can be a real chore. Moving forward, your choice is sticky, meaning that when you go wide it will persist across your session."