The convention, as I understand it, is about government bills. Prior to the government of 2004 to 2006, a lot of private members' business was not votable. In other words, it was to create discussion around a new subject and get Parliament thinking about it. If you were lucky, you would put a bill forward, it would be debated, and in the next session the government might pick it up and make it a government bill.
But I sure hate having the committee strangled by private members' bills. I call it everybody's private hobby horse coming forward in a bill, and to set aside an important study you're doing for a private member's bill.... I don't want to do that. I don't mind a government bill.