Once you get the hang of it you do begin to wonder how you managed without it
When designing new sites I tend to start with the index page as normal and build it as a complete static page to look exactly how I want it to look "compiled". I then work out which areas of the page are the ones that will be repeated throughout the site, I then cut out those areas and paste them into the individual include files and include them back onto the index page. Some are obvious targets, header, footer, navigation, etc.