[pluralsight] Clarify allowed qualities guessing rationale

youtube_dl/extractor/pluralsight.py

@@ -139,6 +139,9 @@ class PluralsightIE(PluralsightBaseIE):
             AllowedQuality('mp4', ('low', 'medium', 'high',)),
         )
 
+        # In order to minimize the number of calls to ViewClip API and reduce
+        # the probability of being throttled or banned by Pluralsight we will request
+        # only single format until explicit listformats was requested.
         if self._downloader.params.get('listformats', False):
             allowed_qualities = ALLOWED_QUALITIES
         else: