I can’t think of a good reason…
My colleague Mark Bodley has drawn my attention to this KB article: Content Index status of all or most of the mailbox databases in the environment shows “Failed”. He has recently experienced this on an exchange 2013 CU5 estate, and, during the course of his research, has seen evidence that it occurs in CU6. My money would be on it persisting in CU7 as well. He points out that while the article states “all or most” of the databases will be affected, he only saw a minority of databases suffering.
if you read the article you can see that the problem is caused by Exchange failing a permissions check on an AD security group called “Content Submitters”, because it doesn’t exist. The fix is to ummm… create an AD security group called “Content Submitters” and grant full access to “Administrators” and “NetworkService”.
I can’t think of a single reason not to go ahead and create that group as part of an install. If you’ve already got Exchange 2013 up and running, why not create the group anyway? That’s one less cause of failed databases you need to worry about.