Pass benefits for Comair are pretty straight forward. You can get on any flight listed in Delta's timetable provided there's a seat. You can get ID90s on a few other carriers... I think Southwest, American, and a few others were on the list. Also, some carriers would honor our pass cards at other than ID90 rates. Comair gets the same pass bennies as mainline Delta guys. Delta was very generous with us.
ID90s (for Industry Discount 90%) are stand-by passes that are discounted 90% off the full-fare walk-up price for the flight. You can often pay less and have a reserved seat if you shop around on-line. ID90s sometimes are good, usually though only as a last resort absolutely-must-get-there backup plan. Most airlines in the U.S. have ID90 privileges with just about all the other US airlines.