- Level 1 Gank
- Smoking into Rosh
- Gaining Control
Level 1 GankWhile this is used to get a quick kill, a morale boost from the first blood, and to give your team an immediate advantage, it also has other purposes.
The main reason I see to use the level 1 gank is to find out where the enemy trilane is going to be. Especially in cases where you either want to force trilane vs. trilane (e.g. you drafted Undying and want to Aggressive Trilane against them), or if you want to dodge their trilane. Even if you don't manage a kill in this situation, you've guaranteed a better laning phase through information collecting (which is always one of the most important pieces of any RTS game).
While you're smoked, you can also put up wards safely.
GankingFrequently you'll see supports pick up Smoke with their starting gold. Often this is used to gank mid once their carry has been established in the lane and no longer needs as much support.
However, there are other uses in the midgame for this item. One of the main uses is after a big item pickup, for instance a Blink Dagger. This will essentially guarantee a kill for your team because the other team has no idea you have the item yet.
You'll also see Smoke ganks come out when you find a key hero out of position (e.g. a carry farming the jungle). This gank will set them back in terms of farm.
Smoking into RoshThis is the most common use you'll see in pub games. Usually an Ursa/Lycan will Smoke before going to Rosh to guarantee that he is not seen by Observer Wards.
But, you'll also see it in pro games to sneak in there all together and quickly kill Rosh before the other team has time to react.
Gaining ControlWhen your team needs to get some sort of advantage to do a push, or to stage a comeback, Smoke is often a vessel for doing so.
For instance, if you need to siege the opponent, but it's not feasible in a 5v5 uphill fight, then picking off a key target with Smoke can give you an advantage.
On the other hand, if your team is behind then Smoke can be used to give you some map control. Smoke up, pick off a key hero and force the opposing team to fall back. Now your team has some room to farm, get wards up, etc.