Are there any risks to running a service as the admin (and login) user on a Windows 10 machine? For instance, will the password be stored on disk in a manner accessible to someone with physical access to the machine? Obviously there is the risk that the service may run code as the user, too, but I don't know if that would be worse than running as SYSTEM.
As for why I'd want to do this, I have several hundred gigabytes of files encrypted with EFS, and I would like to back up these files. This requires that the backup service be able to read the files, which it cannot due to the SYSTEM user not having the appropriate certificate. Adding the certificate for the SYSTEM user to these files would be rather suboptimal, as that certificate is essentially not encrypted at rest - which then removes any protection EFS might provide. Running the backup service as the user in question allows access to the files.