I like them when I have access to an eink display. I find reading for an extended periods of time on an average display a little tiring.
It's also nice to be able to cheaply purchase books that can be hard to come by. I was looking for A Roadside Picnic for a while at local bookstores and couldn't find it for example.
One issue I've encountered though is being spoiled by choice. Buying books on sale and keeping them in my digital library. It can make picking a new book a bit challenging