[dsr_]

It re-executes your previous command -- this time with root privilege.

If and only if you meant to do that, you're fine.

[Firehed]

Why else would you type it in? I can't imagine many people saying "hm, that command I didn't intend to run didn't work. Maybe I should run it as root instead."

Hopefully if you're in a NOPASSWD user/group, you know what root can do if you're careless; if you're not, there's yet another point where you'd have go out of your way to do damage with this shorthand.

[dbaupp]

The "only if" part is false: it is certainly possibleto be fine having done sudo !! without meaning to do it.