Undoubtedly, before the creation of all the buttons in Photoshop was a very broad practice. This allowed to display them in different browsers without any problems, because not all browsers had previously supported the same gradients and so on. In addition, all kinds of gradients, flashing buttons were previously in fashion. But this one was also flawed. It consisted in the fact that it was very difficult to create an object that, when resized, maintained a normal texture, so most of the sites were of a fixed width and height of objects.
Nowadays, almost all browsers began to support gradients, animations using CSS and so on. Many bugs were fixed and even a new Microsoft browser - Edge began to support all styles normally. According to this, if you know how to impose a normal button with CSS , it is better to do it only with the help of it, so that the object is flexible and your site does not load for 2 hours due to the huge number of images.