in which situations it would be OK, and what exactly would it imply?
It would be okay in the USA.
If you said it in the UK, it would imply that you are using American English.
As has been said in comments, this may or may not be understood in other places than North America. If it is understood, then it is through watching American TV and cinema.
In Britain, I would expect, "You're welcome", "No problem", "Not a problem", "That's okay" or even just a smile or a nod of acknowledgement.
Depending on the exact context, some traditionally-minded people in Britain might say, "My pleasure" or "It was nothing", or (very old-fashioned) "Think nothing of it".
In Australia (I'm not an expert), I might expect, "No problem", "No worries", "You're welcome"
See comment by @mdewey. In Britain the phrase "No worries" is increasingly used. If my memory serves, it came into use here after the release of the movie Crocodile Dundee where the phrase was used a lot by Australian characters.
You can search the script here http://www.allreadable.com/mv10758EEG8