As part of the ongoing transition towards decarbonisation and decentralisation of energy systems, collective self-consumption and Energy Communities (ECs) have become increasingly relevant in Europe as several concepts have emerged, framed by two EU directives. However, their potential to become a standard organisational model is still uncertain, as the structure of ECs may jeopardise existing market principles and increase system costs. This article provides an overview of the state of the art of national transpositions of ECs by reviewing recent studies on European implementation and energy-sharing strategies, particularly regarding peer-topeer trading. These approaches raise fundamental questions about the financial viability and development of the electricity system and are compared to the latest experimental findings. Hence significant barriers are pointed out and key implications for self-consumption and EC policies are given to elaborate adapted national conditions for ECs and to ensure adequate tariff reforms. This paper identifies the need for further investigation on national approaches to enable the efficient and sustainable development of ECs. Moreover, in the interest of the consumer's well-being and the well-functioning of the market, a multidisciplinary approach should be integrated that incorporates adapted regulations and appropriate framework conditions for ECs according to the prevailing economic and social context.