Is it safe to unplug a iPad or iPhone without ejecting first? [duplicate]
What is best practice? It is always best to eject removable media (iDevice, external storage, etc.) before disconnecting it.
Is is 'safe' if you don't eject first? Mostly yes, but not guaranteed. As long as there isn't an active file transfer, or the device isn't otherwise being accessed by your computer, its pretty much fine to do. Though there is a chance for corruption, I don't think I've ever encountered it over the numerous times I've done it - accidentally or not.
Aside: last I checked, the most Apple USB buses supply a measly 0.5 amps, so you'll get much faster charging performance if you use the supplied power adapter with your device.