Dithering is still more important than is commonly known, even with 24-bit "true color". For example, imagine that you had a gradient that goes from white to black across a 1920x1080 monitor. 24-bit color means you only have 256 levels of color, so a naive gradient implementation will result in 256 discrete bands of different grays, each about 8 pixels wide (about as wide as this "w" character).

You might not thing that you'd notice that, but it looks surprisingly bad. Your eyes would immediately notice that there are "stripes" of solid gray instead of a smooth continuum. But if you apply dithering, your eyes won't be able to notice (at least not easily). It will all look smooth again.

In a situation like this, I like to use "blue noise" dithering, but there are scores of dithering methods to choose from.