What is the point of reporting “descent” and “ascent” in these chains?

The Meeting Condition in Muʿanʿan Hadith: Muslim’s Rejoinder and Route Comparison

• Every chain’s soundness is set by its minimum number of narrators
• Narrators sometimes accurately specify longer and shorter transmission routes
• Every longer route necessarily involves tadlīs al-shuyūkh
• The phrase refers only to age differences