Personally, I keep everything.
If you only want to keep the finished movie and not the source clips, I would suggest storing out a high quality master file of your final movie. In iMovie this would be in Apple Intermediate Codec. In Final Cut Pro X, I would use a ProRes 422 master file. From the master file, you can make compressed copies in h.264 or whatever is current for use in iTunes, the Web, etc.
Even if you do not keep your event clips, I strongly suggest that you keep a good copy of the original files from your camera. In other words, a Camera Archive, which is the compressed files from the camera rather than the larger Apple Intermediate Codec files for editing which are in the events.
This is not an easy question. Here is a recent thread on a similar topic.
If I export a Project as Apple Intermediate Codec, I then import this 'finished project' master file into iTunes for viewing and burning to DVD? So that will create another file and nearly double the memory capacity required?
OK, I see. I might need to just take your approach and keep buying bigger hard drives to store it all. The first 14 years of my kid's lives fit on 1TB. (I've been a bit slack the last few years). I guess I can upgrade my iMac's hard drives and Time Machine backups. (Plural, but putting it that way it's almost the cost of a new computer! 2TB or 3TB hard drive + 2 external time machines so I can swap an A and B Time Machine off site at dads).
The best format for iTunes and iphone/iPad is h.264.
The reason I suggest keeping a master copy in Apple Intermediate Codec is so you have the option of converting to a future format from a relatively uncompressed version of your movie. Many people will just save the h.264 version and be done with it.
The reason I keep my original events (and I have a lot of disk drives) is so I can make movies in the future. I'll give you an example. I might make a movie of my daughter's 4 yr old birthday party. It is a nice movie and it is in iTunes.
Well, when my daughter went to College, we could not be with her on her birthday, so I made a movie that went back in time from her 18th birthday, 17, 16, 15, 12, 10, 9, 8, 6, 4, 3, 2, 1, and some hospital footage from the day she was born. She really liked it, and it was easy to do, because I still had all the Events.
This is easy to do in iMovie, but it takes a lot of storage space. Only you can decide if it is worth it.
If I had saved AIC or DV versions, I could have also created my movie of many movies, but I would be limited to the footage I used in the original movie. This is usually OK, because I would probably use the best stuff anyway.
There is no one right answer. There are just tradeoffs that you can make.
Thanks. Your daughter's birthday story is exactly the sort of thing I'm considering, so thank you for sharing.
One last question: if I were to travel down your path and save everything in iMovie for future reference (using keytags to mark my kid's birthdays for exactly that kind of birthday compilation, etc), how would I go about upgrading the hard drives? I've heard editing movie footage can create a lot of wear and tear on the internal hard drive, and for this reason some people only do their iMovie stuff on external drives. Do you do this?
And if i were to only to save my iMovie stuff to an external drive, what's the best way to copy that drive to another that I might store off site, and only bring back home briefly for a quick back up?
iMovie doesn't really cause a lot of wear and tear. The reason a lot of video professionals use external drives is that your internal drive holds the Mac OSX Operating System, so the internal drive is quite busy managing the OS and managing the swapfiles, which are swapping applications in and out of memory to the hard drive. While the OS is doing a lot of small quick reads and writes, the iMovie is doing a lot of long reads and writes, because video is big and you tend to get big chunks of it at once.
This makes a lot of sense, but in my experience, in the recent Macs, the internal drive works just fine. If you have enough memory (say 4GB plus - (I have 16GB), then your internal drive is not having to work all that hard for the OSX.
Personally, I do keep my events on the external drive, but it is more for space reasons. I do not want to fill it up with video. I keep my internal drive for other stuff, and keep videos on the externals.
The best way to copy stuff to another drive is in the User Tip that I wrote. Be sure to do all moves from within iMovie. If you move stuff in the Finder, it breaks your projects, because they can no longer find the clips they need. Here is a link to the User Tip. Note the part that says if you are doing Keywords, do a COPY rather than a MOVE. Then you can go back and delete the copy you no longer need later.