I am one of those luthiers that likes to use open headstocks. They have more room than slot heads to get in there when you are changing strings.
Like slot heads they put the tuner buttons in an ergonomically superior position to see and turn compared to solid headstocks. We all are used to solid headstocks but if you think about it why would you want the easiest strings to break and the hardest strings to tune to be the most fiddly to access?
If those treble string tuner buttons were bolt heads on a car engine they would be described as "*expletive* hard to get to".
Open headstocks are lightweight making it easy to avoid making a neck heavy guitar.
Finally, open headstocks do offer an alternative ascetic that is very contemporary. Since contemporary guitars are in a golden age it's nice to have a headstock style to flaunt it!
When I looked at this picture I realized I forgot to add how nice it is to have such easy access to the torsion rod.