In a real work environment you are likely to need to share files with others. In that case you should allow write access by the group and choose a group that includes other people who deserve access. See your site policy for more detailed guidance on this.

As for 666, I have always suspected that the permission scheme was deliberately chosen to make rw access to the world work out to be 666 specifically to make people think twice about doing so. If it wasn't intended then it was a darned convenient choice...