Many computers start counting down a safety stop at a predetermined depth, like 20 feet, and some also start counting down a deep stop at a predetermined depth, like 60 or 50 feet. Many people will feel comfortable omitting or shortening these in the event of an emergency, but some will not.
Many? How about some NDL computers have built in timers. The multi gas trimix computers I have dived have timers on the main screen... You just count off three minutes - they also don't like ascent rates greater than 30'/min. Safety stops are not "mandatory" irrespective of whether the computer has a countdown. Current/tide change may be a good reason to get to the surface without a safety stop.