when do you start thinking about message queues?

hey folks, ive been seeing message queues pop up in a lot of system designs lately, and im curious about when they actually become a necessity versus just an optional add-on. were building out a new feature that involves decoupling a couple of services, and im weighing whether to introduce rabbitmq or kafka early on or if we can get away with simpler synchronous communication for now. what are your key indicators or criteria for deciding that a message queue is the right choice for a given problem