I can tell you from personal experience, in an environment where we are moving to multiple instances on huge workhorse cluster systems, that this is a critical thing to know. Integration Services won't work properly if you need to use the MSDB portion of IS storage. That said, if you keep packages in the file system and only use SQL Agent to run them as jobs, you don't even need Integration Services. You can supply all of the detail in the job creation to run the package without use of Integration Services (which is the preferred method at our shop, though not always possible with third party apps, thus the criticality of today's question).