There's a marginal difference between searching the contents of all the books on earth and the indexes/glossaries of the books you have on your shelf. The latter is a great productivity boost, while the prior is most likely infuriatingly pointless.
"Oh great, I found this exact algorithm I need in this obscure book which has been out of print since 1986."
"Oh great, I found this exact algorithm I need in this obscure book which has been out of print since 1986."