Whole ownership does (theoretically) mean that owners of a property can use it whenever they choose. If they wish to visit their property at a moments notice (as long as it isn’t being rented), they can do so. This is obviously a positive for those who arrange vacations at short notice.
With Fractional Ownership, usage terms are laid out in advance and therefore owners may have to plan their vacation time around their allocated usage weeks for a certain year. If this is a problem then fractional may not be for you. However, most people need to plan holidays well in advance plus fractional owners can exchange weeks with other owners if mutually beneficial to both parties.
With whole ownership, owners pay the "whole" cost. Whether it be purchase or running costs, the financial burden is far greater. Many people who own properties outright, may only use their property for a month or so every year and therefore seek to rent it out when they are not there. In many cases, rental income is vital to assist with the operational & mortgage costs.
Usually, a large percentage of the rental income, will be taken by the rental / management agency in return for promoting the property, meeting the guests and handling all maintenance issues. The outcome may not be as financially rewarding as forecasted, especially considering you are letting strangers into your property.
With fractional, you do not have to worry about your property being empty (and paying for itself) when you are not using it. The idea is you buy a share for the amount of weeks you intend to use. Also when other owners are using the property they will treat it with much more care than holiday-makers who are simply renting. It is their home too and they want to see the property in good order as they have a stake in its overall value.