If you're seeing this option on your score submission page, then the organizer of your event has allowed athletes to perform the prescribed workout at a lower scale.
There may be 2 or 3 variations of the workout
Prescribed - you performed the workout as it was prescribed
Intermediate - you adjusted the workout based on the mid version of the workout
Scaled - you adjusted the workout based on the easiest version of the workout
How does that affect my ranking?
If you perform the workout Prescribed, your rank for that workout will always be better anyone that performs a scaled version.
If you perform the workout as Intermediate, your rank for that workout will always be lower than a Prescribed score and higher than a Scaled score
If you perform the workout as Scaled, your rank for that workout will always be lower than a Prescribed and Intermediate score.
Scores are notated on the leaderboard as
(i) if a score was performed with an Intermediate variation and
(s) if a score was performed with a Scaled variation
The example leaderboard below illustrations how ranks are determined.