Decoupling between publishers and subscribers is the biggest one. Being able to store messages while consumer is down. Last will messages are very convenient. A

Decoupling between publishers and subscribers is the biggest one. Being able to store messages while consumer is down. Last will messages are very convenient. Ability to authorize on topic level. All of that is very useful in my use case (networking and IoT equipment in the middle of nowhere in rough conditions that can go down a fair amount).