message queues: when to use them, when to skip them

So, I've been pondering message queues for decoupling services. We've definitely used them for background jobs and when services need to chat but don't need instant replies. That works great. But I'm wondering about the flip side. Are there times when a message queue just makes things more complicated than they need to be? Like, if things are super straightforward and synchronous is fine, doesn't a queue just add another thing that can break? What have you all found? Any specific pros and cons you've seen when deciding if a message queue is the right move for your system?