So, I work with radios operating in the 450-470 MHz spectrum (among other bands). How these frequencies are assigned is complicated - they are usually coordinated, but aren't necessarily exclusive. So, for example, when setting up a data telemetry link between two points, you should go through the coordination process to find a frequency that is clear in the area you want to operate in. Frequencies are currently assigned on a 12.5kHz spacing, so in that band there are 800 channels (for various reasons, a given business or individual's application isn't eligible for all of the 800 - they may be reserved for public safety, or for low power voice, etc).

Two issues arise from this limitation - you may not be able to get as many frequencies as you want (perhaps you want 10 channels to have overlayed networks and/or repeaters). You also may not be able to get a 25kHz channel, which used to be the default assignment, and now is special request/justification only due to band crowding. Smaller channels = less bandwidth = less potential applications. In extremely crowded areas, there may be no available frequencies at all (or they may be limited to a few watts, reducing range and potential applications).

Amateurs currency have access to 420-450 MHz, an even larger band. If any of that were to be re-assigned, in theory it would be easier to get more channels or larger channels (there's no technical reason you could operate at 50kHz or 100kHz in that band, for example). Opening up even 2 MHz of spectrum could mean tens of thousands of additional stations could get on the air or new or existing licensees could get larger, faster channels.

A common misconception is that all commercial frequencies are auctioned off for geographically exclusive operation - this isn't true in this band and some others. A 10 year license is available to any American citizen, business, or municipal organization for about ~$500.

edit: I am aware this article is about 144-148 MHz, not 400 MHz. 150-174 MHz is more or less adjacent to the 2m band, and is handled by the FCC in more or less the same way as the 450-470 MHz band.

> Amateurs currency have access to 420-450 MHz, an even larger band. If any of that were to be re-assigned, in theory it would be easier to get more channels or larger channels (there's no technical reason you could operate at 50kHz or 100kHz in that band, for example). Opening up even 2 MHz of spectrum could mean tens of thousands of additional stations could get on the air or new or existing licensees could get larger, faster channels.

I worry about slippery slope it would create. AFAIU, opening up those few MHz out of amateur band would let tens of thousands of commercial station to pop up... and the band would get crowded again, leading to pleads for the amateurs to release couple more MHz, until eventually amateurs are no more in this part of the spectrum.