kcbuds2

As the title says..
I have a HTC sensation just updated to ics but it has slowed my phone down, lagging opening and closing apps, when browsing the net it takes a few seconds to stabilize. imo ics is rubbish the only good thing is being able to unlock phone with your face..

so I want to know what's so good about rooting your phone? what are the risks,advantages and disadvantages ?
thanks