Sightstone vs Ruby sight stone

I am confused as to the reason for ever upgrading to it costs 800 gold for 250 extra health and the ability to carry around 1 extra ward? other then buying it as a litteral very last item I don't see the point in this because most of the time the 4 wards regular sight stone has is enough to get me by before im going to back anyways, I would understand if maybe spending 800 gold had the added effect

+400 hp 5 wards Unique passive- stealth wards you place last 25% longer (45 seconds) and see 10% further

but otherwise I don't really see the point in ever upgrading this item I mean 800 gold for a support can go to so many better uses elsewhere why upgrade it for 1 ward in your pocket and 250 health?