How should I store my loaded Hi Power at home? Cocked and locked? Condition 2 or 3? Should I keep it at half cock with the safety on? The answer depends upon your personal situation and if you intend it to be a self-protection weapon. Frankly, I keep my Hi Powers and other single-action automatics in but two conditions.
1. If loaded and outside the safe, the pistol has the hammer fully cocked and the thumb safety engaged.
2. If unloaded and in the safe, the hammer is all the way forward.
I do not recommend lowering the hammer either fully or to half cock over a loaded round. The reasons are several, but the main reason is that over the long term, doing this will probably lead to an unintended discharge. We may be extremely careful, but we only have to make a mistake or let the hammer slip one time for this to happen. Usually, I find that folks asking this question are doing so out of concern that leaving their pistol cocked 24/7 will hurt it. It will not. The mainspring will not be weakened by leaving the Hi Power fully cocked and letting the hammer forward only when shooting or dry firing, etc. FN uses quality springs in the gun and the spring is fine compressed so long as it's not compressed more than it was engineered to be. I've personally left my old "duty Hi Power" cocked and locked for a period of several years except for when shooting, dry firing, or cleaning. It's fine to this day.
This Mk III 9mm Browning was used for several years in police work. On duty, it was cocked and locked and at home, it stayed the same way. Leaving your Hi Power in this condition does not weaken or damage anything including the mainspring. It also encourages not letting your trigger finger "gravitate" toward the trigger until you are truly ready to fire the weapon.
I can think of no compelling reason to store a Hi Power with the hammer forward or at half cock with the thumb safety engaged.
Some folks do opt to keep the gun in "Condition Three" when not being carried, but still being used as a home defense weapon. The reason I've been given is that if they wake from a deep sleep, they prefer to have to rack the slide and chamber a round before the pistol can be fired to insure that they don't do something unintentional while half asleep with a cocked and locked Hi Power. You decide if that works in your personal situation.