A perfectly exposed photo with the wrong thing in focus is still a missed shot.
Single-shot AF (AF-S) locks focus once — best for stationary subjects. Continuous AF (AF-C) keeps refocusing as long as you hold the shutter, tracking movement — essential for sports, kids, pets, wildlife.
Focus points matter as much as the mode. A common habit — "focus and recompose," locking focus center-frame then reframing — works fine at narrow apertures, but at wide apertures (f/1.8-f/2.8) it's prone to subtly missed focus, since recomposing shifts the focal plane just enough to blur a subject's eyes. The more reliable habit: move your focus point to where your subject actually is.
Most cameras from recent years include automatic eye/face detection, which has made "focus and recompose" largely unnecessary for portraits — turn it on and let the camera find the eyes.