Would probably depend on which CAS category you shoot. If your CAS category requires one handed shooting with handguns (Duelist, Gunfighter, etc.) it may be hard to transition to that style right after shooting IDPA or any other two-handed (gun is held and shot with both hands) shooting sport, especially since the handguns involved (SAA type vs semi auto or DA revolver) differ so much in feel and operation. On the other hand, any shooting activity is bound to provide some benefits, especially if you are a Traditional Class CASer.
Now, if you are under age 40 or so, you're probably still mentally and physically flexible and adaptable enough that the above advice doesn't apply to you.
