Currently, the smoke is client side, not server side. Smoke also cannot be seen from a certain distance, this means it's only useful during mid-range combat.
Smoke grenades are a throwable device packed with a mixture of potassium chlorate, lactose, and typically a dye for signalling. The chemicals mix with air to create a smoke screen that temporarily removes battlefield awareness.
~ In-game description
Update #59 (Season 15 - Update 15.1)
Smoke grenade deployment sound and visual effects are now synchronized
The deploy sound stops ten seconds before the smoke cover fully disappears.
Smoke cover fadeout starts when sound effect is stopped, so player can start being visible from five seconds while inside smoke.
Update #38 (Season 6 - Update 6.2) - vN/A
Decreased fuse time from 3 seconds to 1 second.
Pre-release #32 (Season 4 - Update 4.2) - vN/A
Throwables Friction Adjustment
Adjusted the friction force of throwables to make rolling movement more consistent and predictable.
Friction force has been increased to slow rolling speed and cause them to roll a shorter distance after impacting surfaces.
Smoke Grenade Improvement
Smoke grenades are now more accurately synchronized across all players and observers.
Previously, smoke grenade duration for the viewer would start when coming into viewable range (1 km) of the smoke grenade. Smoke grenade plumes will now end at the same time for all players/observers.
Pre-Update #24 - vN/A
Smoke Grenades are spawned at a higher rate compared to other throwables.