In reply to Terence.

DB Queries are expensive so let's say you have a lot of plugins installed that are making a lot of DB Queries. Your site will require more memory and may not perform as well as you would like. You can build an exact identical HTML copy of a WordPress site visually and the performance/speed difference will be huge, but of course the HTML site will be static and not dynamic. If you create a DB for the HTML static site and then run all the same Queries you are running on your WordPress identical site copy then the speed/performance of both sites is going to be almost the same. All about the total number, frequency and type (lots of data processed vs just a little data processed) of DB Queries that are being run.