In the old days, .675 was an FCC designated emergency channel usable by any licensee for /emergencies/ (this is back when one applied for TWO of the main frequency pairs, and they were listed on one's license -- you could NOT use any other main frequency; if your radio was, as many business radios of the era, only a two-channel radio [A/B toggle switch], and your license did not include .675, you had no access to the emergency frequency. If you specified .675 as one of your two frequencies, then it was available for general use. When I got licensed, the Maxon GMRS 210+3 was a desirable radio: it had the 462MHz interstitials (in 1-7), .675 (as channel 8), and channels 9&10 were "shop" programmable for the two frequencies on one's license. [While FCC regulations specified a radio shop must do the programming, they included the programming manual -- take the back off, press some button to enter #9 mode, rotate dial to select frequency, press button to enter #10 mode, turn dial to select frequency] Repeater vs Simplex was handled by a front-panel button which would toggle the current channel's state.
Note the age of my call-sign -- a 3x4 vs the current crop of 4x3.