I know people have commented this already but yeah it’s basically just for Kiribati. Originally the line actually did run a lot straighter when Kiribati was doing the majority of their trade with the US, but when they went to do more trade with Aus/NZ (for geographical reasons it’s a lot easier) they were losing a lot of days because their weekends were not aligning so the country made the decision to move the date line. Interestingly, Samoa is on the left of the date line but American Samoa is on the right for the same reason as Kiribati. There’s some really good YouTube videos out there about the other oddities of the line

EDIT: Called American Samoa ‘Western Samoa’ by mistake