On the microscopic level where the record grooves lie, the sloppiness(and you can feel this) in the pins that hold the stylus in the cartridge body translate out to big and loose tolerances. When you glue it tight those tolerances become more accurate tracing of the groove. It is not a small difference, some of these guys who claim to mod cartridges, thats what they do and it sounds much better. Here's one, a cross-bar mounted on the outer body of the cartridge front. Made of tiny brass I-beam that is used for model railroad track. It helps stabilise the cartridge on difficult to track passages, acts as a torsional counterwieght.