It's the time each transmission spins on air. With the default long fast, a 230 character message spins two seconds being transmitted.
If you are in a vehicle, for example, another vehicle could go in between you or a building could come in between you, etc. And the transmission could be broken.
By using faster presets, your node spends less time transmitting, which is less time that interference can occur.
So it is the baudrate then?
Yes. On long fast, the transmission speed is 1.09 kbps. On short fast, the transmission speed is about 10 kbps.
A message that spends two seconds being transmitted on long fast takes a quarter second on short fast, for example.
Any tradeoffs to all he higher baudrate?
Power consumption?
Actually, power consumption should be lower because of the fact that the transmitter is not turned on for as long.
The main trade-off you will see would be shorter propagation distance.
In an urban environment, that's not going to matter that much. But in a rural setting, it might matter.
