Sometimes bracketing makes sense... For example: you're in the studio, where you normally use three or more lights, and where most of the 120 and 4x5 slide film is used... The main light is what you meter incident, but the effect light, and the background light, are aimed in a different direction, So, sometimes it doesn't matter too much if the main light is a bit higher or lower on the final slide, and LOTS of times you end up deciding which slide to scan and process depending on shadows and/or highlights rendition instead of that of the main light...
And even outdoors, light and its measurement change a lot, because of quality and not only quantity... If the sun is a bit lateral you need to expose for more light, or with the sun right behind, some other times for less light because of too harsh light reflection on certain surfaces... For all those reasons bracketing for 1/2 or 2/3 stop both sides is highly recommended for the best possible results. Only with slide film, and only that close to one decided incident metering.
Cheers,
Juan