What's the difference....
I'll take a chance.....
All CALL is usually resrved for emergency type events where all the units (Fire/EMS/Police/public works/etc) on a system need to hear message. If a unit is on talkgroup A, their radio is probably programmed to also listen to ALLCALL.
DISPATCH is where day to day unit control is run. Usually group specific, i.e. fire dispatch, police dispatch, etc. Often radio traffic is then switched to a TAC or OPS frequency as part of the dispatch assignment
COUTYWIDE is probably a area talkgroup for those few times you need to talk across the region to others. It may be being used as a general admin/talk channel, depends on system guidelines
tom