Polygraph Language or PGL is used to describe experiment configuration and workloads. Some believe that PGL is what makes Polygraph so flexible and powerful compared to many other benchmarks. Many also believe that PGL makes Polygraph more difficult to use for the beginners.
If you use recent standard workloads only, you do not need to have indepth knowledge of PGL because the workloads are structured so that only a few key parameters have to be specified in an obvious way. However, if you want to modify standard workloads or design your own ones, you will have to learn PGL.