An arc fault occurs when electricity is allowed to arc-to travel via-a spark usually from ahot wire to a neutral or ground wire.

 Arc fault most often occur in a lamp or appliance cord , and it also happends in electrical box as well , when a hot wire with damaged insulation touches a bare ground wire.

 this arc ( spark) can creats a fire hazard, A afci breaker will likely stut off  whole circuit. afci is more reliable , for that reason afci breaker are now  requird by must local codes for many city and county.

 It is good idea for bed rooms and living room as well.