PubNub offers a message delivery service with a maximum message size of 32KB, which is sufficient for various applications including IoT solutions, geolocation updates, and real-time gaming leaderboards, but can be limited for more data-intensive uses like chat messages or cognitive analyses. The blog post provides insights into calculating message size, emphasizing the need for message testing and adaptations when dealing with larger data, such as using multiple messages for large texts or converting images to base-64, which adds overhead. PubNub's global presence and patented architecture ensure rapid message delivery, typically within 250 milliseconds. Additionally, the platform offers features like message persistence, mobile push notifications, user presence detection, access management, and customizable functions to enhance user interaction and application management. PubNub encourages experimenting with its SDKs to find optimal solutions and offers various resources and support for developers to build and potentially open-source their projects.