Although its gone in and out of fashion to hate on sumo, every single lifter should try it as
1. if you are competing, you might be better at it than conventional
2. even if you prefer conventional, its a valid accessory
3. having another large compound you can chip away at is going to help your lifting longterm
What is the big advantage?
When we've helped people program or done our own programming, getting a lift that you can put heavy load on glute, abductor and adductor complex is extremely helpful.
Your adductor is the big muscle inside the thigh, and one of its jobs is rotating internally and externally the leg. You often see people unable rotate through the hip on the ascent of a squat.
Many people program Copenhagen Side Planks or pause squats to help this area. Both are great, but we like the sumo as primary.
What if I can't get into position?
Pull off blocks, as high as you need to get into position. You want to be able to force your knees out the whole time.
Will it help my conventional?
Yes, from our experience, it is a very solid accessory. Even if you main lift is sumo, we'd recommend conventional deadlifts as a accessory.
The longer you life, the more likely you will have a lift 'stall' or a small niggle that makes it feel off. This is why longterm we like to build the conventional and sumo together, so when one isn't great, you can focus on the other.