Earlier quoted context omitted.
A huge number of small annoyances during "normal" usage of a computer. Issues with sleep, displays, hi DPI, even my wallpaper and fonts don't always display correctly...
Just don't buy "Windows certified" laptops... Upd: why downvotes? My Librem 15 and Lenovo T400 both work flawlessly for many years. They are designed for GNU/Linux.
The battery thing is really a killer for me.