free rein vs wiggle room

free rein

noun
  • The absence of constraints; freedom to make decisions. 

  • Loose rein(s), as of a horse. 

wiggle room

noun
  • The opportunity to make alternative decisions or to pursue other courses of action, especially any involving only minor changes to one's present situation or course. 

How often have the words free rein and wiggle room occurred in a corpus of books? (source: Google Ngram Viewer )