Lightroom’s main advantage over Photoshop + Bridge is workflow efficiency. It brings importing, library management, keywording, non-destructive editing, publishing, and printing into one application with a unified interface, so you spend less time switching between programs.

While Photoshop + Bridge can cover many of the same tasks, Lightroom is designed specifically around photographic workflow. Key tools such as histogram, tone curve, white balance, and exposure controls are readily available in one place, making routine adjustments faster and more accessible. Many actions that take several steps in Photoshop are quicker in Lightroom.

Lightroom also includes some photography-focused features that may be more convenient or not as directly available in Photoshop workflows, such as lens profile corrections mentioned for Lightroom 3.

So the biggest benefit is not necessarily that Lightroom can do something completely impossible in Photoshop + Bridge, but that it streamlines common photo-management and editing tasks into a faster, more photographer-oriented workflow. One community response also noted that Lightroom is generally less expensive.