More screen space with the taskbar on the side. I only use taskbar icons so I don’t have (or want) programs stretching across the whole bottom of the screen, they just bunch up together in the top corner. Also 99% of the websites I’ve used in the past decade have had big spaces on both sides to allow for smaller resolutions, so losing that couple of blank centimetres means I gain a couple vertically that actually get used by the site.