Thus any variation in the voltage is transmitted to 24 other lines. It should be between 4.25 and 5.25 volts. If it is less than this, the 24 signals won't get their proper termination voltage. Usually this is set with a jumper. This is because the power supply is dirty thus this line has spikes.
Spikes cause erratic termination which in turn cause bus problems and lockups.
Remember, this signal is the source of termination power for 24 other signal lines. If just one end is on, the voltage drops by the time the signal gets the last device on the other end, which brings it below specifications. In summary, there are many factors which influence the signal stability of the SCSI bus. With the faster speeds of the new SCSI systems, the SCSI bus is pushed to its maximum tolerance. This means you must make sure everything conforms to specifications.