It needs to take both into consideration to be a good investment in some sense: it might make financial sense to not spend a large sum of cash on a down payment

It needs to take both into consideration to be a good investment in some sense: it might make financial sense to not spend a large sum of cash on a down payment, but invest the money and continue renting (even if the cost of renting is significantly greater than the (property taxes + mortgage - tax savings) would be for the same property), as long as the returns of the invested money are greater than what you are losing on renting. A friend of mine did the math on this for a few property types in Northern California and it worked out to be fairly close in most cases. With that said, there seem to be pretty significant stability and psychological gains to owning a house that may outweigh financial considerations of this kind. That is doubly true if the investment + renting option is within the same ballpark as the ownership option.