The deposit is designed to cover any possible damages caused during your stay.
If, at the end of your stay, no damages are identified, the owner will return the security deposit to you within 8 days. Otherwise, the cost of repairing any damages will be deducted from the security deposit and part (or none) of the remaining amount will be returned to you within 60 days of your departure.
Amount of the security deposit:
If you have signed a "bail mobilité"
The lessor cannot ask you to pay a security deposit.