It used to be the case that all EBS storage was meant to be initialized to avoid the first-time-access penalty, which becomes a noticeable overhead as you start dealing with larger and larger volumes. Nowadays, the situation has improved as new volumes need no pre-warming (ref: http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ebs-initialize.html); however, one should still consider the added delay to the boot process (if the volume is needed at boot time) against any potential performance gains.
For very large volumes, initialization might be prohibitive, but in any other case, it is certainly worth doing. Or if you run your own database servers on EC2, then you should definitely consider pre-warming volumes regardless of size.
You could use the suggested command-line steps to measure time spent performing this type of optimization (refer to http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ebs-initialize.html).