Is there a potential downside? Yes. Just because a search engine sees something as Creative Commons doesn’t necessarily mean that it is. Here at MakeUseOf, for example, we’ve had at least one photographer threaten to sue us over an image he didn’t realize he himself licensed as Creative Content. He backed down when we pointed this out, and it’s one example resulting from thousands of blog posts spread over a decade, but know that this isn’t without risk.
I used clipart a LOT for newsetters and other documents. I don't always want a photo - clipart is often better at getting an idea across quickly, and I didn't need to worry about copyright because I assumed it was OK to use without permission as it was a part of the MS package. The BING option is terrible - very juvenile and hardly extensive with fewer than 50 options. And by-the-way, most of the online sites for "accessing clipart in MS Word 2010" still say to go to insert then click on clipart. Really - we hardly need such basic instructions when they aren't even correct anymore!
As an artist I resent some people's assumption that original art from my abilities and imagination, which I have sacrificed a lot to develop, should somehow default to public property. If we require artists to participate in a money economy their art belongs to them. Copying images and not following the copyright owners permissions to the letter is stealing, outright. And deep pockets like Disney has taught individuals that the hard way.
This is TERRIBLE! Besides being able to edit vector images like Will mentioned (which is important for those of us who don't have graphic artists available to create custom images or the budget or time to buy that service ad hoc), you could also search for style "families" (different graphics that were all in the same style). There was a huge range of files and styles in the collection and it was much faster to find what you need than to do a Bing search. Plus, you knew that everything there was free and free to use, without having to worry about CC license issues.