There was quite a bigf difference between England and France considering the treatment of POW's.
NB didn't have a clear view of how to treat them but he couldn't allow that they would be guarded at the cost of the State. So the rank and file were employed through the country, whereas the officers were kept as guests. The POW's, who swore a parole, were even allowed to join their town of village of destination without any guards but did have to join the local gendarmerie posts of the towns they were passing.
A very interesting book on this subject is written by Léonce Bernard "Les prisonniers de guerre du premier Empire".