Forma Questions for those who own the Forma and smaller Kobo devices

Dear Kobo users,

For a long time, I've been considering getting a Kobo Forma. I have told myself that a bigger screen is nicer, because:
1. You don't have press the next-page button as often.
2. You can see more words at a time (font size staying constant).
3. You get a better reading experience with PDFs.

But now I wonder if I really need the larger Forma. So my question for those who have a Forma and a smaller Kobo device:
1. Why did you end up with multiple Kobos?
2. When do you use the Forma? When do you use your smaller Kobo?