I understand that legally speaking, gurantor of a lease would take responsibilities if the person signs the lease, for some reasons, cannot meet his/her obligation. However, I do not consider it a big deal to co-sign the lease if you are the only person he/she can ask help from and you trust him/her. My hu*****and pretty much co-signs all his students' leases, for the reason that, as he puts it, whom else they can ask for in this foreign country.