Owning and running a car requires annual inspections and servicing to keep it running optimally and for you to get a heads-up on any potential issues before they become too problematic to resolve. Managing your team requires the same inspections: a yearly check-in to make sure everyone is happy with progress and to track where they want and need to go. It is an opportunity to make any corrections and for people to understand the areas they are excelling in, the areas in which they need improvement, and any new opportunities you or they would like to explore.
You may already be doing reviews or some version of them. Most people dread that time of year, because it creates a huge administrative overhead, depending on the number in the team, and can result in a very superficial/rushed experience with no value coming out of it, except to tick a box for HR. Often annual reviews are tied to a time of the year when a company determines compensation adjustments and bonuses. This has the benefit of having everything done at the same time, but it also means everything is done at the same time!