User blog comment:BorosPaladin/"Must Have" for Season 3/@comment-81.51.16.158-20121217101233/@comment-5441738-20121217141102

If nothing else, you can sell the sightstone, sure. But it gives you wards not only on the cheap but redeployably. DOn't need a ward in that brush anymore? Plant it somewhere else and refresh the timer for the low cost of one Sightstone charge!

I can see how some champions could want to sell it in the mid to late game, but the extra visibility can be incredibly useful. Just with one or two wards I've been on teams able to gank half the enemy team as they move into position to try to attack us. It's pretty incredibly, IMO, what a half-dozen well-placed wards can do.