DeclarativeWorkflowAutoStartOnEmailEnabled Why FALSE by default

I found following code will let the workflow associated with the Incoming Email Enabled Library be started automatically when it is set to started when i new item is created.

$spWebService = [Microsoft.SharePoint.Administration.SPWebService]::ContentService $spWebService.DeclarativeWorkflowAutoStartOnEmailEnabled= $true $spWebService.Update()

But i wonder why Microsoft made this setting to be false by default? Is there any specific performance reasons or does it have any hidden difficulties?

My client keen to know about it before setting it to TRUE.

Any help is greatly appreciated.Thanks in advance