The default behavior for an ACD queue is that when an agent is on a non-ACD call, ACD interactions will still alert on that Agent's queue. An ACD will interrupt a non-ACD call, and when the agent answers the incoming interaction it puts the non-ACD call on hold, causing some confusion.
Some contact centers prefer to use the Utilization settings to determine whether an incoming ACD interaction should be allowed to interrupt a non-ACD call. Checking the box for Include non-ACD conversations does just that. By default, that will prevent all ACD interactions from interrupting a non-ACD call.
In practice, most contact centers will probably change the Utilization settings to allow Chat, Email, and Social Media to interrup a Voice interaction, so that an Agent who is on a call can still perform ACD work on the other interaction types. Keep in mind, the Utilization settings are global, not limited to a specific queue, so the settings need to be configured in a way that accommodates all of the queues.
Another possible drawback to turning on the setting is that agents may figure out that if they place a call from the PureCloud client to their cell phone, it will prevent them from receiving ACD calls (and other ACD interactions that are not allowed to interrupt a call) - something for contact center supervisors to keep an eye on.