There are a few advantages of owning a whole house humidifier. A whole house humidifier would be able to keep the entire house in a humid condition which is not something that a small portable humidifier can do. 

Having a whole house humidifier is convenient in the sense that you don't have to refill and maintain many portable humidifiers. Rather than spending money buying a few portable humidifiers and placing them all around the house, you should get a whole house humidifier to do the work. You will save money and the work is more efficiently done. 

Moreover a whole house humidifier would not need as much maintenance as small humidifiers, which require changing of filters and descaling the tanks every now and then. Some whole house humidifiers also have a filter to change but you only have to change this one filter. This also contributes to the cost saving. 

Benefits of Whole House Humidifier

"In general, a whole-house unit is an install-it-and-forget-it item. It's integrated into the blower system on your furnace, drawing water directly from your water supply. There are a few different types on the market, including a sprayer that injects mist into the airflow inside your ductwork and a foam cylinder that rotates in a water tray, with air blowing through and around it.

Pluses: 

The whole-house system's greatest advantage is that it requires virtually no maintenance and keeps your entire home at a set humidity with just a one-time setup. Because it draws water from your plumbing system as it's needed, you never have to fill it or worry that it's not humidifying because it's run dry. It's virtually soundless, and initial cost is a fraction of what most portable units cost. In addition, most whole-house humidifiers literally cost pennies per year to operate..."