Why should the fine adjustment knob be used only with LPO?

The fine adjustment knob should be used only with the low power objective (LPO) because it allows for precise focusing without the risk of crashing the objective lens into the slide. At higher magnifications, using the fine adjustment can lead to damage both to the slide and the lens due to the increased proximity. The coarse adjustment knob, which moves the stage significantly, is suited for initial focusing with LPO, while the fine adjustment is designed for subtle tweaks in clarity once the specimen is roughly in focus.