Your character works hard to earn gold—plundering tombs, killing things and taking their stuff, accomplishing dangerous feats of derring-do. So why would you spend that money on a building rather than on a shiny new suit of armor or a magical sword?
A stronghold offers benefits that are designed to be equal or superior to the equivalent expenditure in arms and equipment. These benefits grant stronghold builders (and their parties) resources, bonuses, powers, and abilities which directly affect them, and which make their tomb raiding easier.
Haven. Unless the Narrator deems otherwise, you are always able to use your stronghold as a haven.