Everything broken gets on the live severs new champs come out broken most of the time now sej with her insane stats I don't even want her nerfd to the ground its good that shes back in meta but this is ridiculous...
To find bugs.
PBE is a shitfest, You don't get a good idea how how balanced Sejuani is if a Bronze sejuani plays it vs a challenger jungler and gets stomped, or if a challenger Sejuani stomps some poor bronze player. The function of PBE is to make sure everything works properly when it hits live. So we don't have to deal with as many gamebreaking bugs.
because taking advice from pbe players has worked so well in the past 
To make sure that 
changes don't make it live due to complaints.
To try to find some bugs before it hits live. It's impossible to use the PBE for balance testing. It has worse matchmaking than normals and queue times take for ever
I don't know man. When every fiddle get a buff on the PBE the always revert or change it.
