I do keep up with the advanced option recording the number of rewatchs, but I know a lot of people don't know that exists. It'd also be cool to be able to go to a user's watchlist and see the rewatches alongside the CW. Perhaps even with the count of number of times rewatched. It can really help you identify users you relate to and/or the quality of the drama in question.
It could also be helpful on a personal level with keeping up with what episode of the rewatch you are on.
For one, in case the platform you were watching it on removes it or geoblocks it while you are rewatching.
For two, because some platforms (such as viki) don't always make it easy for you to tell where you are in a rewatch.
For three, if you pause your rewatch for any reason.