Some years ago I had all my books available in printed form and were sold via Lulu Publishing through their online store. I also had a number of printed copies myself that I sold via Ebay. Over the years however there was a decline in sales so I changed from printed editions to ebooks and sold them via Kindle Direct Publishing removing them from Lulu first. Kindle also had the option to do printed books but I found that to be far more cumbersome than Lulu due to the formatting structure of ebooks being vastly different than its accompanying printed form. Although having said that I still have a number of printed books available via Amazon.
Well now I appear to have reached a similar juncture as I had with Lulu in the past. My sales have dwindled of late and it's only my very recent books that sell. There's still the option to release my old titles for free via Amazon but that option is only available for five days per year, per book, so while I may get a sudden increase in readership it's only short lived and doesn't always guarantee a review.
The other option of course is to place my books on my website for free. I have experimented with this in the past and I currently do this for my micro-short stories and fan fiction, but I'm still in two minds about it. With some of my very early work, my first novel for instance, I'm perfectly happy to do such a thing but with some of the larger novels it feels a little strange.
There's also the advantage that I have more control over a web based book and can alter the entire formatting with ease. In the same way that a movie is released at the cinema then later released on DVD with lots of extras I could remove my older Amazon books and convert them into web based stories with extras. This is also an advantage for people without a Kindle who can read them using their computer or mobile phone.
Anyway whatever I decide it will only apply to my older books, I'll still be writing more titles for the Amazon Kindle in the years to come. I'm not planning to retire just yet.