This info is not something to be taken lightly and might even make database creation an out-of-hours job!
From Exchange 2013 RTM onwards, whenever a new database is created, the information store service should be restarted for proper memory management. The warning is not displayed in 2013 RTM, but the CU1 exposes it.
Even if you don’t restart the service, the database will get mounted and will be operational. You can move mailboxes to it and perform regular admin tasks, but caching won’t be efficient. The requirement to restart the service is due to the new memory management model and Managed Store in 2013. The store calculates the amount of memory it needs to manage all of the databases only on two occasions – server start-up and when the information store service gets restarted.
This requirement will change the way admins manage databases currently and will push for an approved change request (CR) to create a new database and have it fully operational. Check Tony Redmond’s article where he explains the topic in detail.