For laundry stains Joe'* hand cleaner works better than WD40 and won't slain clothes. Plus it smells a whole lot better. Joe'* smells like pink bubble gum.
In the automotive environment, using WD40 will usually result in immediate lubrication. Then its propellant dries, leaving an oily residue that attracts dirt. The dirt tends to absorb and retain moisture leading to corrosion, so that you have now corroded the part you were trying to protect.