11gR2: Performance with NVL or NVL2 is slow

My Oracle Support article ID 2093132.1 for the document "Slow Performance With NVL or NVL2 Referencing PL/SQL Function Even When Ignoring the Function's Result" directs us not to an issue but to a basic fundamental part of PL/SQL that is certainly worth checking out!  Without looking at the document, can you guess why this is happening?