At the major auction last February, companies spent over $81 billion to secure the spectrum that was once allocated to satellite TV. Verizon won 3,500 licenses for a whopping $45.5 billion, AT&T secured 1,621 licenses for $23.4 billion and T-mobile—needing less C-band than the others with its Sprint acquisition of 2.5GHz—won 142 licenses for $9.3 billion.

Despite the ongoing controversy surrounding the use of C-band near airports, U.S. mobile carriers wouldn’t be nearly as far along building 5G networks without it. Here are the reasons C-band is so crucial to 5G networking.

C-band hits the “sweet spots” of speed and distance.

Spectrum for wireless networking is divided into three types of bands: low, mid and high. Low includes 600, 700, 800 MHz and has the most resilient signal but supports low bandwidth and throughput. Conversely, high band (also known as mmWave) has the highest bandwidth and throughput but travels short distances and can be obstructed by things as commonplace as rain or high winds.

C-band is part of the mid-band spectrum and the perfect compromise of high bandwidth signal resiliency, making it ideal for supporting a sprawling 5G network. While T-Mobile’s 5G plan incorporated its own 2.5GHz mid-band with its low band 600MHz for 5G, Verizon and AT&T used more mmWave to build their networks. They quickly found out that it wasn’t the right spectrum for the job and mostly suitable for “hot spots” of lightning-fast connectivity in urban areas. Thanks to the C-band auction, Verizon and AT&T could pivot strategies and keep the competitive landscape afloat—effectively saving 5G in the US.

C-band is more spectrally efficient than most LTE bands.

People tend to think about 5G in terms of high speeds and lower latency, but spectral efficiency is another equally important metric that doesn’t mean much to anyone outside of telecommunications, but it will soon. It means the maximum bits of data that can be transmitted to a certain number of users per second with acceptable service.

This isn’t just important for the reasons stated above; it also allows mobile carriers to use that extra bandwidth for over-the-air backhaul instead of very costly cabling between the cell site and the network. Since C-band is one of the rare swathes of the spectrum all major U.S. carriers are using for 5G, we are poised for a spectrally efficient future.

The mid-band, especially the C-band, has a significant impact on aggregate 5G expansion. Based on its availability (there is a lot of it), spectral efficiency and combination of high bandwidth and signal strength, C-band can help overcome the challenges presented to carriers for growing 5G networks. This could open the doors for a lot more 5G in-building wireless deployments and system upgrades in the near future, especially as carriers use aggregation to improve speeds even further in the coming years.