For example, if you have a BMW M51 diesel engine (TDS) that starts fine cold but refuses to hot-start, most generic scanners will show a "needle lift sensor" error. Booklet 17, however, includes a specific "Table 17-C" that correlates internal pump clearance (measured in microns) with fuel temperature viscosity. It tells you that before replacing the injection pump, you should measure the armature end-play. This level of detail is absent from modern one-click diagnostic guides.
Here are the three main reasons this booklet remains a hot commodity on eBay, vintage Porsche forums, and Mercedes-Benz enthusiast groups: bosch booklet 17