What is the benefit of a Split-Grip on an ice rod?
Benefit.....
It makes the rod setup lighter.....which can make it feel more sensitive for those that feel the bite.
It allows for extending the handle length without having to ad the full weight of a complete handle since the gaps are small.
By having the but end it can help to balance an ice Rod/reel setup.
Some setups have the back butt that removes to become a hook removal tool.
Overall.....I think it really has more to do with a company trying to be different and the market didn't have a split grip out...so they shrank down a top end open water style Rod and charged a premium for it.