Having an index file in all of your directories also keeps the public from seeing a list of every file and directory within a directory. Without an index file, when someone types the URL that goes to a folder/directory in most cases it will list every file in there. There are many reasons you will not want that to happen.
.htaccess is a faster way to prevent this.
It's easy to overlook something you're not looking for.
This is a site I built for my work.(RSD)
This is a site I built for use in my job.(HTML Editor)
This is my personal site used for testing and as an easy way to share photos.(RLM imported to RSD)