If you happen to have a large collection of workouts that are not being used and you would like to keep that data associated with them you can archive the workout. What this means it will not be available in the workout picker, on mobile and it will be in a dedicated section within the workouts page.
To Archive A Workout:
"Edit" the workout and at the bottom workout screen you will see an option to "Archive"
Once it is archived it will be in the dedicated "Archived Workouts" section on the "Workouts" page.
Archived workouts will not clutter the quick add workout picker or your custom measures data. This makes planning super focused.
To Unarchive A Workout:
In you need to "unarchive" a workout. Click on the workout from the "Archived workout" section on the workouts page. "Edit" that workout and then you'll get an option to "Unarchive" at the bottom.