If a friend of a member of your family wants to visit you in France, this person needs a « attestation d'accueil ».
Is it important ? Who needs one ?
It is compulsory if your friends or family need a visa to come in France. Without this attestation they won't obtain their visa.
If a visa isn't necessary, this attestation can be asked at the customs. If they don't have it, they won't be allowed to enter the French territory.
Does everybody need one ?
Some nationalities don't need this « attestation d'accueil » among them :
- Members of the European community « espace économique européen » and their familly,
citizens from Switzerland, Monaco, Andorre,
- holders of a visa with « carte de séjour à solliciter dès l'arrivée en France ».
If you don't know, ask people at your « mairie » (town hall).