It always makes sense to look at jury instructions at the beginning of a case. In drafting a complaint, plaintiffs' lawyers will learn what evidence they will need to plead and prove in order to get to a jury. Defense lawyers will learn ways of preventing this that might not have been obvious until they took a look at the instructions. (Reminder: Some of the Illinois Pattern Instructions are online.)
The Illinois Pattern Instructions also include information about Illinois substantive law that can be helpful to know at all stages of the trial-preparation process.