This article focuses purely on this subject from a management point of view. Of course technically you be as granular as you like giving access to individual items in a list or the list itself.
However in an organisation of 1000’s that can hardly be recommended, if SharePoint Owners start doing this even on a casual basis were soon to be in a user management nightmare.
Its recommended that if inherited permissions need to be broken for a specific list or item, then perhaps that list and or item should be made available through a separate site where access can be maintained at the site groups level. This can either be done very easily at a site Collection or sub site level, at at this level its much easier to manage.
For example a group of users have a Site Collection, they wish to publish a document to the whole corporation, instead of giving everyone access to that document library or the document itself why not create a sub site Document Workspace and place it in that, and remember when creating the sub site you can specify that you want it to “”Use unique permissions””.