The troops will not walk right next to the building. They will stop approaching the building once they are within range of it.
Flares can be used to flank people who place their Headquarters at the back of their island with very little protection. By using Flares, you can guide your troops to walk around the edge of the island and into the weak spot at the back with the Headquarters.
Be careful when guiding infantry troops together, as Mortars and Rocket Launchers could use the chance to kill all of them quickly.
Flares work well with Shock Bombs if the shocked defense is targeted. This gets rid of said defense quickly.
The higher the level of the Flare, the longer it will last. There are no visual changes.
Old Flare timers disappear when a new Flare is used. However, the original Flare remains.
If the troops reach the Flare before it stops smoking, and the Flare was not dropped on a building, they will turn around and attack the nearest building.
Similarly, if the Flare's timer runs out before the troops reach it, the troops will stop for a brief moment and then target the nearest building.
If the Flare was placed on a building and it is destroyed before the timer runs out, the troops will target the nearest building normally. Any troops that were still approaching the building will stop moving toward it.
Whenever you retreat from a battle, then place down a Flare, your troops will ignore it and keep moving back to the Landing Crafts.
The Flare was once named Signal Smoke and appeared very similar to the Smoke Screen except with colored smoke during beta. It was soon changed to the stick we see it as today and was renamed Flare.