Kindle lets you loan books - if the publisher allows - for a single short period. Get a book loaned to you but something comes up and can't read it in that window? Oh well out of luck!
I think the author has control over that, but I may be mistaken.
This is one that bit me just a few weeks ago. I'd purchased a recent Jonathan Kellerman Kindle book, but wasn't in the mood to read it yet - so I was going to lend it to my wife. Guess what? It wasn't allowed.
This is why, even though it's inconvenient, I strip the DRM from every Kindle book I buy. Because of that, I was able to "lend" the book to my wife without having to go without my own (physical) Kindle for the duration. Yeah, I know - I'm a hardened criminal and should be in the slammer. But I have access to my purchased ebooks and will be able to use them as common sense dictates, with or without Amazon's blessing.
If Amazon ever makes removing DRM impossible, I won't be buying from them.