Power washing a bicycle
Power washing will clean your bike, followed by closely after forcing you to replace all your bearing compartments.  This means your headset, bottom bracket, pedals, and wheels (hubs, freewheel or freehub).  

Do not powerwash your bike.  At all.  With all the effort it would take to properly "cover" all the bearing compartments, then had washing all those areas after, you could have just cleaned the entire bike by hand properly.