Answer:
An electronic diary allows you to keep your data safe and encrypted, so that only you would be able to read your entries. You can make multiple copies of it, so that you'll know that it won't be lost, unlike a paper diary that can be lost, torn or will simply deteriorate over time.
A product like Smart Diary Suite also allows you to track "Life Factors" which can be anything you want - basically they are things that affect your life. For example, you can see how your dietary habits change your mood or how your exercise levels change your sleep. It's really all up to you.