I briefly worked in a public library and the problem they had was that there&#x27;s no practical way to maintain sufficient numbers and depth of subject-matter experts who can answer the subjective assessment such as you list.<p>Ideally one or two shallow-SMEs in each field would be maintained over a region, but that will never happen.<p>So you end-up with librarians making retention decisions based on what publications tell them are the &quot;most useful&quot; books in a topic area and trying to correlate that with check-out frequency.  But those topic areas are coarse-grained like &#x27;history of aviation&#x27; or &#x27;web programming&#x27;.  It&#x27;s a crap-shoot and unfortunately a lot of good books are weeded instead of the dross.<p>My cheap solution:  non-fiction is retained until a updated edition is purchased ( or forever if that doesn&#x27;t occur ), non-curriculum fiction is weeded after 50 loans regardless of replacement.  Curriculum fiction such as Shakespeare probably shouldn&#x27;t be weeded, just replaced.