I believe the title says it all about this blog post.

I love --amend, but sometimes, well, most of times, the commit message is just the same, there is no need to edit it. We are just forgetting to add files or simply fix some typos.

I found out how to keep the message via tab-completion, then I was disappointed, because you have to use --no-edit, no shortened option now for use. I was hoping something like -M.

For me, let Git bring up editor and save and quit is the faster way, but still good to know this option. As for Mercurial (Hg), it has --amend, but no equivalent --no-edit.