The volume of a narrowband signal will be lower. If there are two transmitters on adjacent channels (an unusual occurrence) they'll interfere with each other more than they would on a "compatible" scanner. And you may not be able to enter the frequency of a "splinter" assignment - the scanner may insist on entering the nearest 5 KHz channel - which won't cause a problem, since your scanner is wide enough to receive a signal 2.5 KHz off center.