First you can more easily implement a rinsing cycle. If you are just using a spin clean, you are more or less just diluting the initial clean. With a vacuum stage before the rinse, you are removing the fluid then removing any residue left fluid. The second thing is being able to play the record sooner since you aren't waiting for air drying.
I had the original Record Doctor. I don't see much of an improvement over the V or VI versions. I'm glad the Mk V is still $199. I paid the same price for my Mk I. I wouldn't go back to it from my Okki Nokki, but, any implementing vacuuming is a better way to clean records over wiping with a cloth or air drying.