Is a tool for concealing troop movement and hindering accurate enemy fire.
New players will usually stop and wait for smoke to disperse rather than advance into it, but when your objective is to advance this is precisely what you should be doing.
Should generally be placed on the *enemy*, so as to confuse and obscure their lines of sight, this can also be used to indicate enemy positions, to encourage friendly troops to move to that position to clear or encamp. Sometimes it is appropriate to put smoke on your own troops to conceal their presence or activities.
Can be fired almost continuously with the presence of two or more ammo packs.
Launching 40mm and hand grenades produces a tell-tale smoke trail along the trajectory of the projectile, this can be concealed by foliage or structures (as demonstrated here).
If you see someone in a concealed position firing smoke as cover: give them an ammo/health pack and while their smoke is in effect immediately advance to the objectives they are clearing a path towards; do not attract fire to their position by running around and firing small-arms indiscriminately.
Keep in mind that large areas of smoke usually contain hand grenades thrown by both friend and enemy, so move quickly to objective, cover or flank, and expect close quarters combat.