The sprocket change has to do with the winter tire project. I`m not looking for any performance gains, only some more room for the rear tire. The problem is the gap between the swing and the tire. With the first tire (120/90-18) there was zero clearance with the mud guard attached.
The second rear tire (110/100-18) was almost good to go with no mods, but I wanted to make sure I got enough clearance so I spent the extra 12€ for a smaller sprocket.
The job itself is very easy. You need some slack for the chain, which requires loosening the rear wheel, but thats quicly done.