As long as your spot weld guns are servo-driven (not air or air-over-oil driven), go ahead and use the maximum CNT 100 for every spot weld where you can get away with it. With a properly-mastered servo weld gun, the G2 (servomotion group 2) motion will take care of the necessary "FINEness" of the spot location accuracy.
Indeed, if you do not use some relatively large CNT value, then the SD an ED distance schedules will be unable to do their jobs.
If your spot weld application is pedestal-mounted/floor-mounted (instead of carried by the robot faceplate), then utilizing the motion option RTCP my help to standardize observed motion.
Example for pedestal-mounted servo weld gun:
24: L P[9] 800 mm/sec CNT100 RTCP
: SPOT [SD=a, P=b, t=3.2, S=c, ED=d]
Example for carried (faceplate-mounted) servo weld gun:
24: L P[9] 800 mm/sec CNT100
: SPOT [SD=a, P=b, t=3.2, S=c, ED=d]
where a, b, c, and d are schedule numbers for Start Distance, Pressure (bite force), weld timer heat Schedule, and End Distance