Expo can make the sticks feel dead around the center if you use too much.

I use it to "soften" the sticks around the center on some of my models, mostly for elevator and aileron. It depends on how sensitive each surface is, and how much throw I have. On sensitive surfaces with plenty of throw expo can smooth out your flying. If you use it in a situation where you don't really need it, you'll just notice that it makes things feel mushy.

On a trainer with the recommended throws you probably would find it more mushy than helpful. As you move along and get more experience, you'll probably increase the throws a bit to liven up the airplane. That's when expo will come in handy. Try 30% first, and make small adjustments from there.