It's mostly important to remember when you're wondering why your mostly-empty queue is still costing you $0.26/month, even if you've got the receive message timeout set to 20 seconds.
Note that this can cause issues: say you have a time sensitive application that receives a batch of "bad" messages which cause failed lambda invocations. The poller will slow down and the throughput will drop drastically, even though your intention might be for the lambda to continue processing at the same rate and power through the bad messages.
This behavior can be disabled with a support request.
Under the hood it might be polling. But it gives the illusion it’s push and it’s bloody useful.
But the whole point about costs with empty queues is important. It is definitely important to understand if you want to customize queues for example with long polling. This parameter changes the time your lambda will poll from your queue