nice

Ultimately as a bit of energy infrastructure something like a propane tank is gonna be similar to underground power lines and things of that nature, be they on the scale of private property to powering entire districts. You save on space and generally speaking to hide it is an aesthetic benefit. It's also kept at a more stable temperature(I live in a pretty stable warm climate so I don't know how Propane copes with larger temperature swings.) And there is ease of access to the tank for any reason you would want to access the tank.(Basically if shit breaks you don't have to dig it up) The costs are: Literally the cost, it takes more effort thus more time thus more money. As stated above, ease of access to the tank. If there is anything in the soil that might impact the tank in any way(perhaps some tank coatings are less corrosion resistant and it's not a good choice to bury them, for example).