Hey look, a non-damage keystone.
* You can hold an additional charge of any trinket.
* Your sight radius increases based on your proximity to your closest ward (+0 at 900 units away and further, to +300 at 0 units away)
* As long as you have at least one ward active and within 900 units of you, invisible/camouflaged units within your sight radius (this includes Stealth Wards) and all units that have left your vision (not sight radius) within the last second are obscured for you instead.
This is a vision-focused keystone that allows the user to have a lot more information than normal.
Holding an additional trinket charge doesn't let you place down wards any faster, but helps you not waste cooldown time if you hit the normal 2 yellow trinket limit. This also lets you hold an extra charge of either a blue or red trinket, giving you more options and flexibility with vision control.
By having invisible and camouflaged units become obscured while you have a ward nearby, this keystone makes it easier to not only know what areas are warded, but also to keep tabs on the movement of enemies who would normally be hard to see. You do need to have a ward active to have this benefit, so it’s not up all the time, especially in the early game. It's also only active for you (your allies don't see them), and it doesn't let you target them with attacks or abilities. You just know where they are. You can also see enemies for a brief moment when they leave vision, allowing you to track enemy pathing as they move through the fog of war.
Finally, having your sight radius increase when close to your wards essentially lets you add the area they cover to your vision area. It’s subtle, but it guarantees your wards get some value, even though you’re right on top of them.