Strafing was quite effective against vehicles, trains, landed aircraft etc. But yes against infantry it didn't make much sense, something about going too fast in shaky airplane trying to hit tiny ants running randomly left and right because they noticed the plane well before plane noticed them

saiya-jin notes that this might be true of attacks on infantry but on vehicles and trains the attacks were very very effective. In particular the German army was reduced to moving by night only in Normandy and the railroads were heavily targeted. Things came to a head in the battle of The Falaise Pocket with artillery and the airforces working together and the descriptions of the aftermath are truely horrific.