CS5.5 is flexible and integrates well into the Creative Suite. In addition to supporting multiple workflows, it's flexible in terms of the power of your system and your audio hardware.
One reason that Soundbooth users fall in love with Audition is the major flexibility and advanced tools it provides. Another is the hands-on experience. Audition's responsiveness and flexible approach to effects work simply makes it a pleasure to use.
Audition is faster, slicker, more grown up, and highly respected. Once you get used to it, you will find yourself thinking more often, "I'll just do it in Audition."
For more on working with Audition CS5.5 (including a section on Audition for Soundbooth users), see my Peachpit course Introducing Adobe Audition CS5.5: Learn by Video. You can also find my online courses and more at 123 Training and my website.