There are many important reasons to be at the right time and place for reporting and accountability. The main reasons of importance are knowing the soldiers wellbeing, information, accountability, movements, and punishments. The first reason being that allows the Chain of Command to know that the soldier is well. Many issues could arise from the soldier not being ok. Not only worries of personal safety to the soldier (aka not dead in a ditch somewhere), but as well to the Army, and OPSEC as a whole. Without the soldier there to verify that they are indeed alright, a waste of precious time and work would be used to track down the soldier to prove his alright. Secondly, many times when a soldier is due to report somewhere, there is information to be given by higher Chain of Command. If a soldier is late or misses the time and place to report, not only will he have missed this information ( or worse yet, interrupted the entire formation), the information would have to be given to him, thusly once again, wasting precious time and work hours that could be better used doing the goal of the mission.
Thirdly is accountability, sometimes the most important part of a formation. For one’s Chain of Command to know all bodies are there and ready to do the mission at hand. A normal civilian job has a clock in and out system, the Army, has formations. Having the head count of everyone present also assists the Chain of Command in knowing if there are any problems.
Failing to report at a certain time or place could also make one miss a movement, whether it be to a range, or a deployment. Missing movement is also grounds for an Article 15(and no one wants one of those).
Finally, reporting can be used as a punishment. In some cases reporting early, (say for missing a formation) is a form of effective punishment to help make sure a soldier is where he needs to be at a certain time. Other times, it is used for extra duty, such as police calls and barrack...