[nraynaud]

I would advise you to at least keep a copy of it. In France that I know best, they could book you up to four hours to find your identity without any suspicion of wrongdoing. But if you carry a copy of it, everything changes, because now they have to either accept it as true or make a case for falsification of papers ID.

[wila]

Same in Thailand. The copy is not legally valid, but helps a lot when asked for your ID. If you show enough respect to the officer then it might be sufficient.

Side note I lived in Thailand for several years and was never asked for an ID.