My rule is basically: If it's visually interesting, such as a good graphic novel or something with good art, I might go and buy the physical book after I've read it digitally. Otherwise, if I intend to lend it out, I'll get the physical copy. Most of my friends aren't e-book people, so it makes sense.

I finished reading the book end May, so around 4-5 months passed and still thinking about it.

The list is a good idea! Might do the same.