tooth bar can:
strengthen bucket lip, keeping it from smiling
provide points for attaching chains for lifting
let you pop rocks out of the ground because one point will dig in and focus the entire FEL force/leverage
increase the capacity of the FEL bucket by about 1/3 to 1/2...my estimate
extend the lip allowing logs/rocks to be chained onto the fel and be moved in a way not allowed by smooth bucket lip
dig into hard ground
dig into a pile of material which has settled/solidified over time
dig into a pile of rock/rubble allowing a full bucket to be obtained
although I can remove my tooth bar, I have done so only once in all my years of tractoring....to me the tooth bar doubles the FEL usefulness, don't go tractor'n without one!!