Your Slate learned from your TMs to create your MT engine. That engine has the knowledge from your past work. Each job has new challenges. Before you start a new project, you can prepare terminology files to force the translated terms based on customer preferences, but you encounter new terms in every project. The terminology-on-the-fly feature gives you the power to save new term pairs to the terminology file as you work. Slate starts using those new terms on the very next segment.