Don't ruin your first impression!!
From Vimeo FAQ: What is video buffering, and how do I do it?
Buffering is a way of preloading the videos you watch so that fluctuations in your Internet connection don't cause choppy playback.
When you play a video, a light gray bar will advance in front of the playhead, showing you how much of your video has been buffered. Your playback should be smooth as long as you're viewing your video within the light gray buffer region.
If you're experiencing choppy playback, pause the video, allow the video to buffer for a few moments, then try playing your video again!