Those. immediately make up the frame and gradually add graphics to it. The style of sites - minimalistic or font. Actively use technologies like Bootstrap, CSS solutions instead of graphics
Your question contains the answer ... What does the psd have to do with this? It is not at all clear ... Use what you want. There are programs - site builders, there are scripts - site builders. psd is convenient to cut graphics for example. But this is not a panacea. You can even make a layout in illustrator ... What is the difference? The customer orders, and you are already choosing the path of least resistance for yourself, so that it is convenient, high-quality and fast.
Watching what a task. For example, for web applications, you can start with bootstrap, where it is more important to just see the necessary information (inventory control, accounting for applications from the site, etc.). Sites focused on the sale of services / product more logical to start with a good design.
And who forbids something? The surest way is to create a template engine.