I wanted to crop a video and post it on YouTube. My first thought was to use iMovie, since it's on my machine. But it didn't support the format of the video I wanted to crop, and the cropping interface was not straightforward.
I asked a friend how they would do it, and they suggested uploading it to YouTube first, and editing it online. I didn't know I could edit it online. A few more things surprised me. First, YouTube supported the format that iMovie didn't. Second, it seemed faster to upload a video to YouTube than to open it in iMovie. Third, the interface for cropping videos on YouTube was easier to use than iMovie.
So, +1 for YouTube, and cloud-based interfaces, and asking experts for advise when doing tasks.