In some cases, you might want to make the subject available. Specifically, for resource mailboxes, it may be useful. In the default configuration, meetings in the calendar of a resource mailbox contain the name of the person that organized the meeting, but not the original subject of the meeting. By allowing users to see the subject of meetings for a resource mailbox, you are allowing them to see who organized the meeting.
The permission to use for showing meeting subjects is LimitedDetails. The command to set this permission on a resource mailbox named Room100 is shown below:
Set-MailboxFolderPermission Room100:\Calendar -User Default -AccessRights LimitedDetails