There are many kinds of file types Bridge can access that LR can’t. If you are primarily working with image files (raws, TIFFs, PSDs etc), then LR is probably all you need. For people dealing with those files and Illustrator, Indesign files etc and have to incorporate them all in various projects, Bridge could be more useful. As stated, Bridge is a browser and can browse lots of file formats. LR is a database for images. I personally never use Bridge, have no need.