Compare data use across video resolutions.
Holding viewing hours constant and varying only the resolution isolates the cost of picture quality. Data scales directly with bitrate, and bitrate rises far faster than resolution: 4K has four times the pixels of 1080p but typically three to four times the bitrate, so the same thirty hours of viewing swings from about 13 GB to nearly 80 GB depending purely on the quality setting.
Resolution cost comparison
GB at any resolution = Mbps x 3600 / (8 x 1024) x hours; extra for 4K = GB at 4K - GB at 1080p
It depends on screen size and distance. On a 65-inch television at three metres the difference from 1080p is visible; on a 27-inch monitor or any phone it is essentially undetectable, in which case the extra data buys nothing.
Because video compression exploits spatial and temporal redundancy, which grows with resolution. Four times the pixels needs roughly three times the bits rather than four, and better codecs widen that gap further.
1440p sits around 9-10 Mbps, roughly double 1080p and half of 4K. It is often the best compromise on a large monitor, giving a visible improvement over 1080p at far less than 4K's cost.