Not necessarily. Depending on what you're researching, volumes can have relevant information on the subject being researched based on the bibliography, notes if any, and the index. You don't have to read the entire book to find the information. And, sometimes, books consulted may not have the information at all or in sufficient detail to be of use.
I'm sure you've come across situations just like described above.
This is especially true with books that have data tables, unit lineage tables, and the like such as artillery manuals and books such as JB Avril's Avantages d'un bonne discipline.