when dont you want to use message queues for scaling background jobs?

hey everyone, ive been thinkin bout how to scale background job processing. weve got a bunch of tasks like sendin emails, processin images, and genin reports that can take a while. right now, some of these are just cron jobs or simple workers. when do you think its the right time to intro a message queue like RabbitMQ or Kafka to handle these, and what are the key indicators you look for before makin that switch, plus the biggest pitfalls ive seen