Accepted solution
Type in PURGE in the command line inside of a model and it'll open a dialog box which will have the objects you can and cannot purge.
Be careful when using this command as it can delete layers and some other objects you want to keep.
I'd recommend testing it out on a model you use for testing that isn't current and wont effect your current job.
In essence, the command is used to clean up the model of unused layers and bothersome blocks.
