On film cameras, exposure bracketing was mainly used to improve your chances of getting one correctly exposed frame.

That was especially useful because you couldn’t review the result immediately, and meter readings were not always reliable for difficult scenes. If the shot mattered and you couldn’t reshoot it, taking a series of exposures above and below the meter recommendation gave you a safer margin.

Bracketing also helps keep framing consistent and reduces subject movement compared with changing settings and shooting more slowly by hand.

Film-era post-processing could do a lot—dodging, burning, and even some HDR-like techniques existed—but blending multiple negatives into one clean final print was generally not the normal purpose of bracketing. It’s possible in principle, but alignment and motion differences make it difficult, and small mismatches can soften or blur the result.

So the classic answer is: on film, bracketing was mostly an insurance policy for exposure accuracy, not primarily a darkroom compositing method.