No, I don't believe FCPX is in the business of destructive editing at all.
It's metadata from what you've got - all the way.
You'll need to either trim rejected parts manually (in some other software) before you import or....
I suppose you could create a temp project, drag your media that has rejected parts into it, and export only the good bits as ProRes and then import the ProRes (with no rejected footage) back in again - and then delete/ignore your original media.
I feel your need, but If I was managing features in the software, i wouldn't add what you want.
If you're that tight for space, then you can manage this situation yourself.
It's professional editing software - no special help for people who don't have the right equipment to deal with what they're doing.
Another thought: if you're not going to be moving your video work from computer to computer, then don't copy the media to your events. FCP will create pointers to your media files – the files that were initially ingested from your camera to your Mac. By not copying the media to event, you don't use any additional storage space.
When your project is finished and delivered, you can save additional space by eliminatng the render files and any media you chose to optimize.
You can use the Consolidation function but it will only remove whole unused clips. If you use any portion of a clip it will be included in its entirety with the consolidation. http://support.apple.com/kb/HT5773
I think furrytoes is funny. He/she sees the inability to delete media as a reflection of FCPx being a professional app. Fascinating. Personally I find it more helpful for me to remember the mantra..."FCPx is not a professional editing app". I've learned to roll my eyes, wipe my tears, and cope with the limitations. I edit for fun and occasionally professionally. I'm about as light a duty professional editor as they come and even I have to shake my head. The kludge to this, as previously mentioned, is to mark whatever sections you want as rejected, then Hide Rejected files. Now drag the good footage, one clip at a time, onto the timeline and export that. Yeah. Seriously. You could do them all at one time if you wanted. Then delete all the original footage and import the footage you exported. Obviously that's crazy talk but if you really, really wanted to cut out some footage, it's the only option I can think of. Of course you'd have to have a good workflow in order not to mess things up and delete footage you wanted to use. You'd have to be experienced. Careful. Professional. So FCPx keeps all the non-pros from messing in their figurative pants. I'll bet there are plenty of people who have been saved by this. I understand the "save them from themselves" concept and deleting footage from a GOP structured media like most of today's footage has may have it's own technical issues.
There well may be valid technical reasons for not being able to delete sections, I recognize that, so in spite of my penchant for )(*&ing and moaning, I also have to admit FCPx may be doing the only thing it can. Dunno...but I sure have a lot of lousy footage that I'd love to be able to actually cut out and delete from my HD. I'm really, really sure the footage taken with my camera left recording as it swung fom my arm is OK to delete.
with respect you are not understanding the fundamental purpose of FCPx. If you want to actually cut and delete media, then either do so prior to importing to FCPx, using quicktime etc, or use iMovie
FCPx creates refence files that leave your original media intact. End of story
I also 'edit for fun and occasionally professionally'. Spend some time examining the difference between iMovie and FCPx, and then perhaps come back to this forum