Lots of people take long videos assuming they'll convert them into time lapses later but their only option is to speed up the video. This can sometimes look a bit like "Fast Forward" instead of an actual time lapse.
This little workaround makes it easy to pick your own speed and interval to turn your video footage into a real time lapse.
EDIT December 2016: QTP is no longer available from Apple. You can still find it from 3rd party places but a different workaround would be:
1. Once you have your images, import them into a video editor such as iMovie or Final Cut Pro or Premiere.
2. Bring them all, in order, into a timeline.
3. Select all and set their duration to each be a single frame such as 00:01 or two frames at 00:02 for a slower timelapse.
4. Group or export that timeline as its own video.
It's a little more complex but lets you be more specific.