Special Sessions are separate from your regular Stack workouts and serve several purposes.  They also count towards your Grit Score.

Speed Priming without Balls: These sessions take approximately 8 minutes to complete and serve as an excellent pre-round boost to your swing speed.  They can act as a replacement to hitting balls after your dynamic warm-up if the course has no range.  They can also be inserted after you've hit irons on the range, but before you transition to driver. These sessions are also an excellent way to bridge the gap between regular workouts if you find yourself short on time. Professional golfers will often perform these sessions on Thursday or Friday, following their round during tournament weeks. 

Speed Priming with Balls: These sessions are similar to Speed Priming without Balls; however, there is an additional set that calls for hitting drivers with ball contact.   These sessions are an excellent way to track your clubhead speed progress in a more realistic scenario.  These can be completed every few weeks on off days, or in the place of a regular training session. 

Return to Form: These sessions are primarily designed to ease Stackers back into training after an extended break. The app monitors the time since your last workout and will automatically recommend these workouts.  In this scenario, you do not need to access these workouts through the Special Session button as the app will call up the workout for you.  However, golfers may choose to perform these workouts without an app recommendation.  Perhaps you had a particularly strenuous weightlifting session the day before and are looking for a less strenuous speed training session to keep the momentum going.

Just follow the app's recommendation. The app will know how long it has been since your last training session and will suggest modified programming if necessary. 

This will be by the way of Return to Form workouts.  These workouts have reduced volume and intensity. The data from these workouts will be saved as a separate graph that can be viewed by swiping from right-to-left in the app. You are not able to "pause" the program to prevent your Grit Score from dropping.  By design, the app's algorithms don't care why you haven't followed the program.