I think the point of an emergency account is preparing for the unknown.  Illness, accidents, natural disasters, etc.  If something unexpected happens and you need cash fast, then you can access your emergency account.  Such as Hurricane Katrina in Louisiana, government provided assisstance, but the money couldn't arrive fast enough.  So having an emergency account would have meant sleeping better at night. 

我们家也差不多是3个月的花费。