Pixel count buys detail density, not clarity as such. Match it against distance, target size and bandwidth/storage together.

• Distance and target: resolution pays off when you need to resolve small targets such as faces or plates. In wide-area overview scenes the perceived difference between 2 MP and 8 MP is modest.
• Bitrate and storage: doubling pixels roughly doubles bitrate and storage demand. One 8 MP channel may consume as much storage as two or three 2 MP channels.
• Night performance: on the same sensor size, more pixels mean smaller photosites and less light per pixel, so low-light performance usually gets worse. Where night image matters, prefer moderate resolution with a larger sensor.
• Bandwidth: many high-resolution channels quickly saturate switch backplanes and uplinks, which is especially visible in remote viewing.

Practical guidance: use 4 MP or 8 MP where identification is required, such as entrances and checkpoints. Use 2 MP to 4 MP for corridors and perimeters where the goal is coverage and behaviour — the balance of image quality and cost is better.