A lot of people hate it but let's take a proper look. You will generally get a much poorer click through rate on the partner network. People think this negatively impacts their Quality Score - it doesn't. It doesn't hurt to have it on, it can give you extra clicks/conversions but you have to be sensible and keep an eye on its performance. So MOST IMPORTANTLY: Always segment your overall stats by this. Just like you might segment brand and generic performance, these two networks behave so differently that you shouldn't aggregate them into an average.