When trying to rent an apartment in France, especially in Paris, I noticed that some landlords ask for your RIB (bank account details). I'm curious why they would need this. What do they do with it? Does knowing those details enable them to debit my bank account?! (Because I definitely do not want to enable that!)
Merely knowing your bank account details is not enough to set up a direct debit, the bank would require your consent (autorisation de prélévement). If you haven't signed such a form, the landlord cannot use the RIB for that (and, incidentally, it's forbidden for landlords to demand that their tenants pay by direct debit, although I can imagine that some do it nonetheless).
But if you fail to pay (or generally owe money to someone), the landlord could under certain conditions get your bank to recover the debt from your account so they might consider that knowing your bank details would make this easier if needed. This would in particular be relatively easy if one of your cheques bounces (but it does involve an huissier de justice in any case).
Also, being able to present a RIB shows you have a bank account and you are not interdit bancaire. A cheque does that too but landlords or real estate agents typically ask for the RIB when you apply, so before you have to produce an actual cheque.
I moved to France in 1989, I opened up two accounts with Crédit Agricole.
I forget if it was taxe foncière or taxe d'habitation (both paid yearly by house owners), one year I was a bit late and went down to pay it only to be told they had already taken it out of my main account.
I thought that a bit strange but they did it, oh yes there was money to cover it.
Since posting the question I have spoken to someone who claims that she provided the RIB and the landlord debited the rent from her account. In this case it was done with the tenant's consent, but she insists this consent was only ever given verbally.
The rental contract did say the rent should "preferably" be paid by direct debit (La redevance sera payable mensuellement et en totalité le premier de chaque mois, de préférence par prélèvement automatique sur compte bancaire), so perhaps that was enough, I don't know.
The landlord in this case was a large company, so perhaps it's not something every landlord can do, but still, it makes me all the more wary of giving my RIB to anyone.