Why do I need Lightroom when I have Bridge?
No it doesn't.
Bridge doesn’t have a brain.
Bridge is a great pair of eyes wearing night vision goggles. Bridge sees things that the Explorer or Finder can’t.
Bridge can preview your raw photos, and read all of the image metadata.
Bridge can also preview the image edits you make with Photoshop’s Adobe Camera Raw.
Graphic designers love Bridge because it can see the contents inside of all kinds of Adobe files without having to open them. For example, Bridge can view all the pages in a multi page PDF file. It can also see the swatches, fonts and linked images inside of an InDesign or Illustrator file.
Bridge doesn’t remember these things though. It just looks at them.
The edits you make to an image using Adobe Camera Raw are stored in a separate file on your hard drive. We call this file a “sidecar”. The sidecar edit file has the extension .xmp. Bridge hides these files, but you can view them with your Explorer of Finder.
If you loose the sidecar file, you loose your edits. Bridge can’t remember them.