Everyone needs a way to quietly unwind from the events of the day.

In the case of Dr. Traits, this takes the form of writing in one or more of his journals.
Each of his three journals serves a specific purpose, and thus focuses on a different topic.

The red binder holds information about his various scientific tests and "patients".
The black binder contains his notes and studies of the genetics, anatomy, and evolution of ponykind.
The green binder, which is also the one that has seen the most use, is where he records the day's thoughts and observations. His personal diary, in other words.

All three binders are protected by magical wards, and are generally stored away in a small interdimensional pocket (or "hammerspace") when not in active use.