When using Git's mail features -- remember, not everyone uses GitHub -- the first line of a commit is a subject line. It's good practice to just think of it that way. If you write sentences in your subject lines in e-mail, I guess, that's up to you. Don't take it from me, read the Tim Pope counterpoint, with eight extremely good reasons for concise subjects in the closing paragraph:
I don't see how this is a counterpoint. tpope says "This first line should be a concise summary of the changes introduced by the commit", and antirez says the first line should be a "synopsis of the meaning of the change operated by the commit"; these appear to be exactly the same thing.
But then, I don't understand the distinction the original post seems to be making between "titles or subjects" and "synopses." A good title or subject for a git commit is a synopsis of the changes in the commit, in the same way a good headline for a newspaper article is a synopsis of the article.
http://tbaggery.com/2008/04/19/a-note-about-git-commit-messa...
Strong disagree with antirez on this one. Even vim filetype gitcommit disagrees. (Try it on the "smart synopsis" example.)