With the release of Exchange 2013, the recommendation around the placement of the mail.que database has been changed.
We have all been placing the hub transport database and it’s log files in a dedicated spindle in the 2007 & 2010 world. At least, that is the recommendation that we gave to customers as a consultant or architect. The latest recommendation for the 2013 servers is that the stateful transport service database on the mailbox servers can be placed on the system drive. The only exception is if the system drive doesn’t have enough space to accommodate the database and the log files.
This will only come into play where large organizations have standard builds for various applications and the drive sizing are different. I have seen organizations where the system drives are not that big, as the build moves the page file to a dedicated drive. In such cases, placing the 2013 transport database on the system drive won’t be a good idea.
In short, the default location for the mail.que is fine in 2013 and there is no need to have dedicated spindles just to host the transport database. This was announced in the TechED NA session by Ross Smith IV.