My Uniden PC 78XL has delta tune, and I modified it to slide between the standard CB
channels. It will swing down about 11 KC and up about 2 KC from the center detent position.
I modified the radio with an external oscillator to work on 29 MHz for Ham AM
use, and the delta tune mod really helps me tune in the guys who don't use the "5s." On the actual CB
band, this ability probably wouldn't be needed because of simpler ways to get on the "A" channels. (Capacitor-10.240-Switch Method)
I think that the original reason for having delta tune on the AM
only CBs was so you could tune in folks whose old 23 channel "crystal-plexers" had drifted WAY off frequency. However, as Loosecannon said, now it is mostly used to put echo, etc. in the place of...