Nominal Spread vs Swap Spread

Hi Friends,

I am struggling to unnderstand these two statements from the CFAI text -

  1. The swaps framework allows managers to more easily compare securities across the fixed rate and floating rate markets. Nominal spread works well across the entire credit quality spectrum from AAA’s to B’s.

  2. However this nominal spread framework does not work very well for investors and issuers when comparing the relatve attrativeness between fixed-rate and floating-rate markets.

Could you please help me out? cheers!