One can see the difference by not only reviewing the output, but even more simply, by reviewing the properties of the plotter provided by the different drivers. PS was created for software on the Mac platform but it can be used on either Macs or PC's. PS has a lot more "options" you can control for images and such while PCL is more streamlined and straight forward b/c it is vector plotting rather than raster as stated above.
Download both PS and PCL drivers for you plotter/printer, then go into the settings of each and compare.
What I've often done is create a PC3 file for each PS and PCL which provides an additional level of convenience to my users.