This is unquestionably the most movement-specific supplementary exercise for the sumo deadlift. It helps to improve:
Muscular strength
Muscular hypertrophy
Muscular endurance
Upper back strength
Grip strength
Lat recruitment
Lockout speed/strength
Generally speaking, train it once per week during any given 3-6 week cycle. Sets and reps can range from 8-15+ depending on your individual needs and goals. Obviously low(er) rep ranges lend themselves better to strength development whereas high(er) rep ranges tend to be better for muscular hypertrophy and endurance.
If you've been around weight training for any length of time, you've probably read or tried an arm specialization routine. There are a bunch of these around with different cool names for what amounts to the same old shit: do a bunch of arm exercises. Yeah, the exercises change and the sets and reps change, but it still amounts to just doing more arm work.