As a librarian I often get asked this question. Both Google and Google Scholar are good tools but sometimes they are not the best tool.
If you only rely on Google Scholar for academic research you'll miss relevant and important research that isn't available for free online. Why is this? Well, most digital scholarly information is behind paywalls and there is a large volume of information that isn't online - both new and old - that Google Scholar can't index.
The nice thing about the Library's scholarly databases is that they cover both open and paywalled information as well as digital and paper resources. This is why librarians recommend them over Google Scholar: they're more complete.