The ordinary queue never gets full. You can create a lossy queue and set a size limit on it. Then the oldest data in the queue gets thrown away if the queue fills up faster than the data is dequeued from it.
Look at the examples for producer/consumer architecture, search the forums for messages with regarding queues for a better understanding of why you would use them. Basically, if you want to pass data from one loop of your program to another to offload some of the work. Let's say one loop does the data acquisition and you don't want to risk losing data, but you also need to do some time consuming processing on the data and also writing it out to a file, so you pass the data to loops that do those functions by way of a queue.
