jQuery allows for various interpretation and coding of the library base. Knowledge of all of the functions and syntax allows for proper and optimal coding.
jQuery can be very complex to those not familiar with all of the syntax. Deep knowledge of jQuery assures quicker debugging and troubleshooting.
jQuery allows the use of various attributes – some of which are interpreted differently by different platforms. Knowing how each function works assures the styling elements are coded in a way that loads the same on all platforms.