Library clauses are stored in some clause library and can be reused from document to document. For information on how to create library clauses, click here.
You can store clauses in different clause libraries: either your personal library, or your organisation’s central library, or the library of one of the departments/groups you are a member of. More information.
Ad-hoc clauses are document-specific clauses that only appear in the document in which they are created. For more information on how to create ad-hoc clauses, click here.
You should only rely on ad-hoc clauses if the clause you are drafting is so specific that you know you will not be using it in other documents. If there is a possibility that you would use it in other documents, it is better to save it in your personal library so that you can still access it but your organisation’s library does not suffer from the clutter.