Low profile - convenient for those who are mobile with their laptops.
While I appreciate the convenience of keeping my Yubikey Nano in the USB port, because of its low profile, nowhere on the Yubico web site are there any instruction about what to do when prompted by a web site to "push a button" on the security key - the Yubikey Nano doesn't have one. So, I have to jiggle it to complete the authentication process. Get with the program, Yubico!