I've heard the full range of experiences.
Some say they group slugs better, some say it doesn't help, others say it's even worse.
The biggest thing to remember is if you get a rifled tube then try A LOT of different slugs.
Just finding the one your smoothbore/IC choked barrel likes may be all you need for accuracy.
On the flip side, every rifled shotgun barrel owner I know can get 3-4" or better accuracy with almost any saboted slugs they buy.
What kinds of groups do you get with your smooth bore?
I can consistently hit a 10" steel plate at 100 yards with Brennekke modified foster style slugs out of my ghost ring sighted Mossberg 500. (I only hunt deer out to 50 yards with it)
They group the best of any rifled slug I've tried.