The baud rate is number of bits per second that get transmitted or received on a serial line. Please see the TTL Serial section of the Maestro user’s guide for more information on serial communication.
Higher baud rates are better because you can transmit data faster, so generally it is good to use the highest baud rate that your transmitter, receiver, and wiring can support.
The baud rate is only relevant if you want to use TTL serial, and it has nothing to do with the number of pulses that get transmitted from a servo controller to its servos.
The transmitter and receiver must agree ahead of time on exactly what baud rate to use (within some margin of error), unless the receiver has an auto-baud detect feature (as all of our Maestro servo controllers do).