The performances of the fifth generation (5G) wireless communication systems are significantly affected by edge cache and transport network. These emerging components bring substantial costs of the placement and utilization, and the evaluation of the cost impact is beyond the capability of traditional performance metrics, including spectral efficiency (SE) and energy efficiency (EE). In this article, economical energy efficiency (E3) is proposed, whose core idea is to take SE/EE and cost into account to evaluate comprehensive gains when different kinds of advanced technologies are used in 5G systems. The E3results are shown when the transport network and edge cache are separately or jointly used. Open issues in terms of modeling the cost, E3optimization based radio resource allocation, and E3optimization for internet of things, are identified as well.