If you use QuickTime to export video, especially to MPEG-4 format, you should try mp4vEncoder, which maintains quality but with a much smaller file size.
There's not much to mp4vEncoder other than installing the binary and configuring the codec to your liking. mp4vEncoder integrates seamlessly with QuickTime and offers you several options relating to how you'd like to encode your video clips. Amongst the major features you have control over are the bitrate, frames per second, macro block decision, worker threads and codec flags.
For many users, however, these terms will be a mystery and there's no documentation or help file with mp4vEncoder to explain what they mean. In addition, you may find it conflicts with other codecs. The Preference panel warns you that some Apple codecs may conflict with it but it does work alongside most major ones such as MPEG-4 and MP4V and provides support for B-frame, MPEG-4, ASP and ffmpeg.
If you've regularly use Quicktime to export video, mp4vEncoder could mean your exports are half the size but still the same quality.