[Q] Q&A- Different radio versions general question topic

I'm by no means an expert, but I have rooted/flashed ROMs on different phones the past few years. This has been my first time running into a phone where the ROMs are picky on which bootloader or radios are installed beforehand. The bootloader/bootstack I understand , but what about radios? Aside from different ROMs requiring certain radio versions, what's the real difference between 12b and 27a? Better signal from towers? Better Lte connectivity?