Website design has come a long way in the last few years and the main reason for that is all of the tools that are now available to the designer. These days you can design a site that can do things that would have been unimaginable just a few years ago. However it is important to make sure that the person who is designing your site knows how to use these tools to the best effect.
Probably the biggest change in the way that modern websites are designed is how interactive they can be. This makes the experience better for your visitors. You can now set up your site so that it shows different content to different visitors. You can use this so that when people come to your site they will get different content than was there last time. It also allows you to do things like show potential customers products that they might be interested in based on the parts of your site they have visited. You have probably seen this one the big shopping sites when they make suggestions of various products. There is no reason you can't do this with your site as well.
Even if you aren't looking to build a site that is this complicated you can still benefit from coding with PHP and MySQL since it makes it easy to change the content of your site. Almost all sites find it necessary to keep adding new content and removing old content from their site. In the old days this required going in and completely recoding the whole page, which was a major deterrent to doing this. However you can now very easily change the content on your site making it much easier to keep it up to date.
Including things like PHP and MySQL is an important part of the design process of your website. It is something that should be included right from the start since you are going to want to integrate it entirely in your site. Therefore it is important to have a designer who understands what it can do and how to use it. These days most designers also do the coding so this should not be a problem but it is something to keep in mind.
It is also important to keep in mind that you want to be careful when you are including elements like PHP and MySQL on your site. A lot of times when people design a site they go overboard and include elements that they don't need or use them way more than is necessary just so that they can add them. In the end this does little more than to irritate your customers. You need to make sure that your site is well designed and that all of the elements are integrated properly so that your site looks good and works properly. It is really quite remarkable how many sites fail to do this.