Microfluidic systems on porous substrates, including paper-based analytical platforms, have attracted significant attention in recent times, primarily attributed to their diversified applications ranging from bio-analytical devices for healthcare technologies to green energy generation and flexible electronics. In this short review, we attempt to provide a concise overview about the fundamental premises of functionalities of these devices, starting from the understanding of flow in single one-dimensional conduit. This can be extended to more complex systems, where an intrinsic capillary action offers the necessary provisions for continuous maintenance of heterogeneous flow over multiple spatio-temporal scales, which essentially facilitates the needs of specific applications. We discuss about few specific applications as demonstrative examples which are solely triggered by the intrinsic capillary action of the porous media. These specific examples delineate the fact that flexible architecture of the devices in combination with the inherent capillary driven phenomena makes it suitable to meet the desired user-specific demands at affordable costs, rendering them immensely suitable for the low resource settings environment.