Imagine you purchased some cool new 4K TV and you want to display photos at maximum resolution from your laptop or perhaps use the display for your huuuge Excel spreadsheets, but your old crappy laptop says it cannot go beyond fullHD (1920×1080 or 1920×1200). Phew. The issue is with the older DisplayPort or HDMI standards.
It is however often possible to force some display mode that can fit with its bandwidth and frequency requirements to the older standards. I was able to play full 4K on an old Sandy Bridge laptop (HP Elitebook 8460p) with integrated Intel HD3000 graphic adapter, however only at mediocre 20 Hz resolution with GTF or CVT 1.1 timings (With CVT 1.2 reduced blanking even 24 or 25 Hz should be possible). At 1440p, it was capable of 30 Hz even on GTF. While 20 Hz is useless for watching films, 24 or 30 Hz may be sufficient (the TV does not flicker anyway, it just displays the same frame 2 or 3 times to fit the native 60 Hz panel…). For a slideshow of photos or working with Adobe Lightroom or Excel, even 20 Hz may be sufficient.