DRY
Don’t Repeat Yourself. It’s sort of a buzzword, but it carries a good deal of truth. The fact is, computers are *built* to automate repetitive tasks - not create them. If it takes a few hours more to program something so that it is easier to update later, by all means do it. Think of the time savings that you would have if on your 300 page website, you wanted to make a simple change to your directory structure, and move your stylesheet. If you designed your page with an included header, the task is trivial. If you hard-coded all that, you’re in for a larger project. How are you going to remember what you have updated and what you have to do still? It’s going to be a real mess, I can assure you that much. Think ahead. Save time.