Energy efficiency, communication reliability, and end to end latency have become the defining performance axes of the next generation Internet of Things (IoT), yet they pull system design in conflicting directions. Mechanisms that buy reliability, such as retransmissions, redundancy, and conservative coding, tend to spend energy and time, while aggressive energy saving through duty cycling, transmit power reduction, or harvesting can erode both timeliness and dependability. This article revisits the conventional view that these objectives form a fixed hierarchy in which one is simply traded for another. Drawing on recent literature in green IoT, ultra reliable low latency communication, wireless energy transfer, edge computation offloading, and the emerging sustainability agenda of sixth generation (6G) networks, we argue that the three-way relationship is better understood as a configurable operating region whose shape is set by workload semantics, channel conditions, and the available physical and architectural levers. We review the metrics by which efficiency is measured, organize the dominant enabling mechanisms by their trade-off signatures, map the requirements of major application domains onto the trade-off space, and propose a unified conceptual framework that treats energy, reliability, and latency as jointly negotiated rather than ranked. We close by identifying open problems in cross layer modeling, measurement, and the standardization of sustainability as a testable constraint. The intended contribution is a clearer vocabulary for reasoning about when a given green technique helps and when it merely shifts cost from one axis to another.