it keeps your car from throwing a code for not having a cat on it. You may not need it...but you might. It goes in the secondary sensor (post cat) and basically just makes it read less emissions by getting it out of the stream of exhaust. They're about $15.
the electronics will be fine. The pre-cat sensor runs the engine...the post cat-sensors just tell the computer if the cat is in working order or not. (to my understanding anyway). If you don't want to eliminate the cats all together, put in some universal high flow race cats.
For me personally, I don't like the smell of running no cats, so when mine go I'll probably throw some high flow cats in there.