message queues why do they start to cause problems

hey folks, ive been using RabbitMQ for a few projects now and its been great for decoupling services and handling background jobs. but, im starting to wonder about the flip side. at what point does the message queue itself become the bottleneck? is it about throughput, latency, the number of queues, or something else entirely? im curious to hear about your experiences with scaling message queues and how you identify and address bottlenecks.