behalf vs grist for the mill

behalf

noun
  • The interest, benefit, or wellbeing of someone or something. 

  • One's role or rightful place; stead or authority. 

grist for the mill

noun
  • Something that is useful or that creates a favorable opportunity. 

How often have the words behalf and grist for the mill occurred in a corpus of books? (source: Google Ngram Viewer )