Why should you not set your transmit frequency to be exactly at the edge of an amateur band or sub-band?
AnswerTo allow for calibration error in the transmitter frequency display; So that modulation sidebands do not extend beyond the band edge; To allow for transmitter frequency drift
Do not transmit exactly at a band or sub-band edge because display calibration error, modulation sidebands, and transmitter drift can put part of the signal outside the authorized segment.