All channels that you define in xLights will generate channel data regardless if you are using them or not. This affects the render times, the size of the fseq files, and the amount of data sent across the network. And remember, with the most common 50ms timing, every channel that you define gets repeated 20 times per second. The more you over-allocate, the bigger the penalty.
You may or may not notice it but its still a penalty for over-allocating universes you aren't using. Reserving some space up front is reasonable, but there is no need to overdo it since adding more channels later is very easy. You can leave gaps in the universe numbers and they don't have to be sequential. Many people make them contiguous because its easy to configure them in bulk, but its not required.
With that said, many habits that people use today are based on limitations of older controllers. Since you are using the Falcon V2 controllers, most of the old way of doing things it not necessary. You can start any port on any channel, regardless of the Universe boundary. In a pure xLights+FalconV2 environment, probably the "Best Practice" is to use Absolute Addressing for everything and stop worrying about universe boundaries. You still need to define enough universes in xlights to handle your total channel count. Just add more universes later when you need more channels. With the Falcon V2 controllers you can put any channel on any port. And with the Virtual Strings feature of the Falcon controllers, you can string models from different universes on the same physical port.
With a pure xLights+FalconV2 environment, just figure out how many total channels you will USE. Then divide by 512 and round up. That's how many universes you define today. Then just add more later if needed.
