Strictly speaking, a dynamic web site involves some sort of processing to generate web pages. However, I also include in this category any site that uses programs (CGIs) for any purpose. The returned pages are not necessarily modified by the programs, but some action is taken based on the data passed to the programs through the browser interface.

Dynamic sites may use a database for any number of purposes.

Advantages:

• Makes it possible to interact with site visitors in ways not possible otherwise; visitors can give you information about themselves which can be retained for future visits. For instance, you might allow them to customize the site appearance according to their preferences.
• Will work on any host that allows you to run CGI scripts.

Disadvantages:

• Programs always takes longer to write than HTML pages. In some cases the programs are already available, so in those cases the extra time is probably insignificant. But if there is any development to be done, the time will be related to the degree of difficulty.
• Some portion of the site may be relatively difficult to edit. Specifically if there are any pages that are dynamically generated, they will probably only be able to be changed by a programmer.

Cost: Moderate to high; $100 minimum.

Yes, I'd like to have a dynamic site.