You decide that you want to end your marriage, and so you file for divorce. You go to the court to file the papers. They explain that the next step is to give your spouse a set amount of time to respond, which you do by serving those papers to him or her. You can officially do this with various service methods, such as the sheriff's office.
However, do you really need to go that far? Maybe, despite the problems in your marriage, you are basically getting along. You hardly think that you need to call the sheriff to serve those papers. It seems too formal and contentious. You decide to just give the papers to your spouse yourself, skipping all the drama.
It may work. If your spouse moves forward with the process properly, it can all be fine. However, you have opened the door to some potential problems.
One reason to have the papers officially served is because then you have a third party that verifies that your spouse actually got them in the first place. They also note the date on which they were served. These pieces of information may become very important if your spouse does not cooperate like you think they will. By serving the papers yourself, you make it possible for your spouse to claim that you did so at a later date or that you never did it at all. It's just your word against theirs.
So, while it may feel overly formal at times, you can see why it is important to understand all of the exact steps you need to take during a divorce.