As best I can figure, the benefits are minimal in economic terms, but big in political terms, which is the entire point of it.
In terms of showing that Global Britain (TM) is free to buccaneer its way across the globe, signing trade deals with all and sundry, and absolutely not missing the EU at all, it's priceless. As long as no one looks too closely at the details, it'll be the headline grabbing national success that the government needs.
It's a bit like a mid-life crisis but in this instance, the Pacific is a Harley/Ferrari/younger lover with daddy issues/hair plugs. It's not being done to address any underlying issues, it's being done to prove a point. Even if it makes no logical sense, it makes perfect emotional sense.
It's Brexit in a nutshell for me, the triumph of feels over facts.
As I said previously, I have no idea which UK export industry is going to greatly benefit from it, and I really don't see which industry that's currently being hamstrung by being outside the single market is going to make up the losses they are currently facing.