In reality, the deal has almost nothing to do with trade: actual trade barriers between these countries are already very low. The TPP is an effort to use the holy grail of free trade to impose conditions and override domestic laws in a way that would be almost impossible if the proposed measures had to go through the normal legislative process. The expectation is that by lining up powerful corporate interests, the governments will be able to ram this new “free trade” pact through legislatures on a take-it-or-leave-it basis.
As with all these multilateral agreements, the intention is to spread its reach through time. That means that anything the original parties to the TPP accept is likely to be imposed later on other countries in the region, and quite likely, on the rest of the world.