The disadvantages are the power supply is usually bigger and more expensive. Another rule of thumb is to look at the efficiency curve of the power supply and place your anticipated load at the maximum efficiency point, making sure you have sufficient design margin using other rules of thumb. These are just my starting ground rules and I will violate them if it makes sense. Field reliability is always my over-arching concern. Others may do it differently.
Comments are always welcome.
Legal Statement Do not use this information for design without independent verification of the information.