@FireDog3105 I find being able to mark a workout as done is useful in the event I replaced it with an outside workout or swapped in another SUF session that day for whatever reason. Also sometimes I just mark a workout done because I want it out of sight - eg. day or week went sideways and I made a decision to skip the workout and not reschedule it.
A good example is the inspiration videos. I have seen almost all of them so I often will try to swap in one that I haven’t seen or go with one of the open or cadence videos and thus mark the originally scheduled workout as done (by substitution). You can easily sort in the app by duration, etc. and find the match that works.
However, some I might leave unmarked. For example, I missed getting Violator in a few weeks ago. I had not done that one in a while and felt I should do it at a time when it fit in properly so I just left it unchecked and then as I came towards the end of my plan I pushed a few things forward and found a good space for it where I can really dial in without affecting any upcoming workouts.
When I first starting doing SUF I tried to get to every workout. However, I found that there is definitely line between suffering and putting myself in a hole that could set me back. Marking it as done doesn’t upload anything to Strava or TrainingPeaks so I don’t see any false data on those apps that could modify stress scores, training hours, etc.