analog vs digital automatic level control
When broadcasting over the air, whether the audio chain is analog, digital, or a hybrid, it's critical not to exceed the peak modulation level that the transmitter (AM or FM) can handle. That's called overmodulation, and it not only distorts the audio, it also can cause spurious signals outside the legal bandwidth assigned to the station.
Preventing that is technically the job of a limiter, which only reduces the signal level when it exceeds that 100% modulation limit. It's a little different from a compressor which reduces excessive peaks, but may also be set to boost the signal when it's too low.
You don't necessarily want a &quot;nearly constant average audio level&quot; if you want to faithfully transmit classical music. On the other hand, if you are doing voice interviews and passing microphones around in a noisy environment, you may want plenty of compression to keep the speech levels fairly constant.
The overmodulation/spurious signals issue doesn't apply to digital streaming, but you still should avoid clipping and distortion, and some combination of compression and/or limiting will be helpful in processing your audio. Most audio consoles or audio software will offer a variety of these options.