Perhaps the best people to answer those types of questions are the negotiators themselves, who are wheeling and dealing at the negotiating table, but essentially it's a matter of reciprocity and setting a precedent.
If you look at perhaps the TPP negotiations, I think there were some comments earlier today about this, when Japan entered the deal, right from the onset it wanted to exclude five agriculture products that are in Canada's offensive interests: beef, pork, grains, rice and sugar. There's no way Canada would have achieved a comprehensive agreement had Japan not agreed to put those products back on the table.
This is a matter of allowing negotiators and the government to have the ability to seek the best agreement for Canada.