The disabled/deleted accounts will no longer be imported, and will no longer be available in the User Profiles record set. That's the short answer. But I bet what you really wanted to know is what effect this will have on the active users' experience and SharePoint sites and documents created by a now disabled/deleted account. I'm no definative voice, but here are a few items I've witnessed after the change and how they are affected:
The dynamic organizational chart: You will see an immediate effect of the disabled/deleted accounts no longer appearing.
My Site: The site is not automatically deleted. This is by design, allowing an administrator to move any content stored on the site first. The My Site Cleanup timer job can be configured to assign administrator rights to the user's My Site to a designated person (such as the user's manager) to facilitate this process. The My Site will continue to show up in search results until deleted.
References to the user as the creator or modifier of a document: these will not be deleted. Each site keeps its own list of users for this purpose. (For example, you may not want Joan to show up as an active employee after she retires, but you still want people to be able to search for documents authored by Joan - she really knew her stuff!)
Site Owner/Library or List Level Authority These will not be deleted. You will need to use an account with higher level or same level account to change these. There are some third party tools that specialize in just such permission control management. While I haven't had to do this, I presume that these types of changes could also be scripted through PowerShell as well.