I was just going through 1-M bidirectional mapping's inverse keyword in hibernate. I searched lot but not able to find example where there should be mandatory to have an inverse true. Just observed the difference in number of update queries fired. Can any one provide some example where it is necessary to make inverse=true.

Well you don't need to use inverse if you are using mappedBy. The only difference is mappeBy explicitly points to the owning side where as inverse=true does not. Inverse does not require knowledge of an owning side in fact their might not even be one. I guess the point I am making is every time you add a mappedBy you are in essence setting inverse-true