Face Detection feature (Also known as Face Recognition or Face Priority Mode) was introduced in 2007 and latest cameras have it. This face detection feature actually sees an object in a scene, lock the focus in it and adjust flash output and exposure so the result become effective and superior.
The Cameras that does not have the “face Detection” feature uses the “Conventional Autofocus systems (AF), Some cameras may have multiple AF zones however still they sometimes miss the object and focuses something else that is around (on a distance or closer), which will results in an out-of-focus picture, might be blurry as well. Meanwhile “Face Detection” technology uses algorithms that has ability to detect typical face patterns in an image then adjust focus and exposure. It’s an ingenious solution.
In short without going on technical details Face detection features is a positive plus in our camera features especially when we are intended to take picture of more than one object in single image.
They considerably do a good job over 90 percent of the time, and they have the great advantage of doing so automatically without time-consuming user intervention So “Go for it if you have choice in your Budget”