Imo, if your goal is competition as a tool for improvement it's important. It's helpful to have as clear a record of your wins, losses and breakdowns of how your matches went, what you did well, what you did that needs work, how you felt, etc...these things all give you a clear idea of what to work on in practice afterwards. There are also a lot of patterns that start to emerge the more you compete that provide information for long term improvement. For example, if you win 30 matches via armbar from guard, you know you have a good armbar from the guard. If you attempt 50 armbars from the guard but only landed thirty of them then you have something to work with and twenty armbar attempts to learn from. Maybe you missed those twenty because the opportunity to armbar was on your weak side. Maybe it was because you were intimidated by certain opponents and didn't think they would "fall for" an armbar from the guard.
The learning can be detecting mental weaknesses you have, physical deficiencies, tactical and strategic errors or technical errors. If you don't record keep in a detailed way then I feel that there are so many wasted pieces of information that you can learn from.