Maintenance Valet or Visiting A Car Shop

I've read several articles about maintenance valet, its benefits as well as the advantage it provides to our car. I think this service is already available in several areas specially along the Metro. And I was able to read some of their reviews about the service and most of it are positive feedback. This service is helpful to all car owners especially if we are busy at work or have other tasks to do. Also, we wouldn't want our car to be neglected as we have other scheduled tasks. With this advantage, is there a reason you wouldn't avail such service? If you have any hesitation and doubts? Feel free to share your thoughts. It would be a huge help.