Delayed Onset Muscle Soreness, despite everyone having heard of it, is still something we still haven't quite nutted out exactly what happens. We "Think" that the soreness part is caused by inflammation as a response to muscle tearing that happens when we exercise, especially when performing exercise we aren't accustomed to, as anyone who has started a new gym program, or even taken part in exercise they aren't used to would know. Usually DOMS is most prominent following exercise that involves eccentric actions, whereby the muscle is brought under load at length, and tends to peak at around 48 hours, but sometimes can make stairs a leap of faith, even after a few days.
Often both trainers, and those getting trained look to DOMS as an indicator of whether or not the previous workout was any good, usually with the trainer taking way too much pride in how much they made their client hurt.
In line with my philosophy on the fact that anyone can make a workout hard-it takes an expert to make in meaningful, we need to look towards the purpose of the workout.
If the goal of the workout was to elicit some muscle building effects, then based on the mechanisms around muscle damage and the like, it makes sense that feeling a little sore post workout will indicate that we damaged the muscle enough to have the mechanisms that rebuild the muscle kick in, allowing for some change in the size of our guns.
We don't know how much a muscle needs to be damaged to cause it to grow, and furthermore, when compared with clinical markers of muscle growth and strength, post exercise pain has been shown to be a poor indicator of gains, with some research even showing subjects reporting increased DOMS with no correlated changes in hypertrophy markers or strength gains.
Given that many bodybuilders tend to mange to continue to grow muscles with a decrease in DOMS, it's fair to say it is probably a poor gauge for how "well" you have exercised, especially when it may interfere with subsequent training.
So expect some DOMS when kicking off a new program, and if building muscle is part of your goal, then for certain muscle groups, DOMS may be relate to how well you are training. If DOMS lasts more than 48 hours, hinders your ability to train, or even reduces your drive to train again, especially when building muscle isn't your goal, then it's probably best to drop the DOMS badge of honour and tame the intensity next time around.