I have never bought a sticker, although I use messaging apps regularly. But I see that girls tend to buy more stickers than guys do.

There is also peer pressure that makes people buy stickers. I have seen that among university students.

I use the free stickers, but won't buy any. I tried to upload my own clip art to line and found that they don't show up with a transparent background like the stickers. There are many apps that make 'stamps' (rectangular clip art for line), I sometimes use them.

Me and my friends among the community bought some stickers. usually we bought those with unordinary style, more like exaggerated gesture and abnormal figures. for example like: "Ike! Inachu Takkyu-bu"

Makes sense! If you use messaging regularly, stickers can be a powerful communication tool!