The Application Information service (AIS), introduced in Vista, is responsible for creating a new process to run applications with elevated privileges. You’ll typically see this happen when running an administrative application while having UAC turned on. If you disable this service, you won’t be able to run applications with elevated privileges, which means you won’t be able to manage your services to enable it again. If you somehow accidentally disable it, boot into safe mode to get access to your services so you can enable it again.