The purpose of shifting taxes from taxes on buildings, wages, sales, to a tax on land, is to give all people an equal share of the earth's land or the rental income from that.
One way to think of it is that there are two pies.
One pie consists of all the land in the world, in the sense of all natural opportunities, including land, air, water, radio spectrum. The land has a rental value. This rental value for land, for example, can be found out by seeing what someone is willing to pay for a given parcel of land. This is often done with long-term leases. Air has a social cost which is the cost to battle the effects of pollution of that air. This "pie" is a gift of God/Nature which belongs to everyone in the world. If someone uses more than their share, they are indebted to the rest of humankind for that use. If we collected all the rent in an area (precinct, city, county, country) and divided and distributed it to all the permanent residents of that area, that would satisfy that debt. One effect of this tax or land rent collection would be to encourage frugal use of land, leaving more for others and for Nature to rejuvenate itself and protect our environment. It also allows communities to set up parks and beaches for the recreation of all.
The other pie represents what humans produce. Examples would be a worker's labor, a doctor's services, the production and showing of a movie, food. This "pie" is due to the individual's or organization's efforts and should not be taxed or divided. It takes nothing away from the common good. It does not need to be taxed. This encourages all people to work efficiently.
The folly of Socialism and Communism is that they try to divide both pies, taking away incentive to work. To the extent that democratic governments tax wages, buildings, and other work, they also destroy incentive to work. To the extent that governments leave land untaxed, they encourage land speculation and they encourage attempts to acquire more land than we need, leaving less for those who need it.
This does not have to be done in the whole world or entire country at once. Many cities in this country and others have instituted a two-tier real estate tax, whereby land is taxed at a higher rate than buildings. Examples are Pittsburgh, Pennsylvania, and Sydney, Australia. The result has been an increase in economic activity and the presence of more affordable housing. See: http://www.progress.org/geonomy/geono05.php