What is the purpose of the Delete Video feature on iPhone?

This is mainly focused on the iPhone, but also on any multimedia device which offers this option. If I'm out and about, and I watch a video on my iPhone, when finished I'm offered the option to delete the video. Really, this is nice, but what's the point of it? The chances of me getting a 700 MB email that I'll need to clear that space up for are pretty slim. On the other hand, the next time I'll need that space will be when I connect it to my computer, where it will then be deleted. Any ideas? I don't see any real practicality behind it.