Originally Posted by HarryT
Conversions are not 100% reliable - they can and do go wrong - and you may not discover this until you read the book. Perhaps you keep on top of your book pile better than I do, but I have ebooks I bought many years ago that I haven't read yet. I suspect that I no longer have access to most of those at the original stores.
Books are small and essentially cost nothing to store. For me it's a no-brainier to store both the original and any conversions. It's minimising risk.
I do keep the original downloads from the stores I perceive as possibly less reliable, and the stores I shop at infrequently. But I think if Amazon, BN, or Kobo goes out of business, there will be enough advance notice for me to redownload the books in my account.
It's not the space per se, it's the clutter. It's confusing to have multiple versions of books scattered all over the place. I have a master list where I indicate where each book came from, so if I encounter a problem that may have resulted from a conversion--which hasn't happened yet--I can redownload from the store.