They say you can't judge a book by its cover. This is very true. You need to pick it up and examine it. To make sure, when I go to a library, I systematically look at every single book, one after another and check to see if it is of interest. In this case, catalogs are useful only to get me into the general area of the books I am looking for. For example, I may have mentioned this before, but I have gone through every single book in the Family History Library in the Rhode Island section, more than once. This is not confined to genealogy books, I do this will all libraries with all books of interest. I have probably looked at most of the books in the Mesa Public Library individually.
OK, so now you are thinking I am really strange. Yes, I am. If strange means that I am thoroughly systematic about doing research about any given topic. There is only one way to be sure that you haven't misses something and that is to look. Is this tedious? Oh, in a way, but it also leads to some very interesting results. If I find an area of interest (like Apache Indians, for example) I will read or at least look at every book in the library on that subject. I know of no other way to make sure you get a balanced view of the information available on a given subject.
With genealogy, unfortunately, I can review all of the books in the Mesa Public Library in about five minutes. This is generally the case with the Phoenix Public Library and the Maricopa County Library also. But, they have other resources that are helpful and I would never know the resources were there without walking the stacks. This idea is more expansive than just staring at the books, it includes becoming familiar with the other library resources, some of which are not easily discoverable.
I realize that some libraries have closed stacks. I understand closed stacks, but to me, it is like being half blind. I can only guess what other treasures there might be in the library hidden behind the catalog and lurking in the closed stacks.