We experience a major paradigm shift in mobile networks. The infrastructure of cellular networks is becoming mobile since it is being densified also by using mobile and nomadic small cells to increase coverage and capacity. Furthermore, the innovative approaches such as green operation through sleep scheduling, user-controlled small cells, and dynamic end-to-end slicing will make the network topology and available resources highly dynamic. Therefore, the density of dynamic networks may vary in time and space from sparse to dense or vice versa. This paper advocates that on density-awareness is critical for dynamic mobile networks. Mobile cells, while bringing many benefits, introduce many unconventional challenges that we present in this paper. Novel techniques are needed for adapting network functions, communication protocols, and their parameters to the network density. Especially when cells on wheels or wings are considered, static and man-made configurations will waste valuable resources such as spectrum or energy if the density is not considered as an optimization parameter. In this paper, we evaluate the dynamicity of nomadic cells in density-aware mobile networks in a comprehensive and articulable way. The main challenges we may face by employing dynamic networks and how we can tackle these problems by using a density-oriented approach are discussed in detail. As a key concern in dynamic mobile networks, we treat the density of base stations, which is an indispensable performance parameter. For the applicability of such a parameter we present several potential density estimators. We epochally discuss the impact of density on coverage, interference, mobility management, scalability, capacity, caching, routing protocols, and energy consumption. Our findings illustrate that mobile cells bring more opportunities in addition to some challenges which can be solved, such as adapting mobile networks to base station density.