More often than not, comments on Git, Subversion, Mercurial or other version control systems (VCS) are totally useless because developers do not follow a few simple rules:
Separate subject from body with a blank line
Limit the subject line length
Capitalize the subject line
Do not end the subject line with a period
Use the imperative mood in the subject line
Wrap the body at 72 characters
Use the body to explain what and why vs. how
(from How to Write a Git Commit Message)