wont effect anything...your check engine light may come on for a while, but mine went off, as for the resonator its about 1/2 - 1hp to get rid of it...and it gives it a little throatier sound if you keep the stock mufflers on, it even gives it a nicer sound with different mufflers on it, the resonator is just a muffler in sense

 

Since it right under the console, I would guess it helps to keep the passenger compartment quieter too.

 

yah, i would imagine so too, but its not too bad in my car with it gone

 

It's also going to depend on what cat you have on as well. When I went to this SLP cat my interior noise went down. When I had the RealTech cat on you had to raise your voice to have a conversation and there was this persistand droning noise in the background.