I tend to use separate groups for each application for two reasons.

1. I can use different music on hold sources when putting callers on hold. This is valuable if the contact centre services different caller groupsv - e.g. callers to a sales line may be played information about special offers, callers to a support line may be played information about alternative contact methods.

2. I am more comfortable that each application has enough CTI ports to cope with the number of sessions I configure.

I think there is definately more to consider than MOH here, you have CID/calling permissions and application utilization/service levels to consider also. Perhaps things that service the business would be more critical to point to a guaranteed group of ports for that application. Sure you could lump everything together, but wouldnt you want to retain control of this crucial piece even if only for troubleshooting sake. Also as for CID and calling permissions, If you were to be servicing multiple clients from one UCCx box, you better believe you wouldnt want to accidentally mix your calls together!