The answer to this question is easy: We need both small cells and Wi-Fi to fit all the traffic generated by smartphone, tablets and laptops.
Historically, the increase in wireless capacity has mostly come from increased cell density. Over the last 45 years, greater cell density accounted for a 1,600-fold increase in capacity, according to Martin Cooper, who led the Motorola team that developed the mobile phone in the 70s. The increase in cell density was mostly aimed at achieving coverage across the footprint.
Today the challenge is different. Mobile networks cover most of the places where humans live, work, or travel. The need is to increase cell density where coverage is already provided by the macro cells. Technological advances and new spectrum allocations will definitely help to improve capacity, but alone they are not sufficient to address the 18-fold traffic increase over the next five years predicted by Cisco’s VNI. According to Alcatel Lucent, increase in cell density will have five times the impact of new spectrum allocation or improvements in spectral efficiency from new technologies such as LTE.