The Plasmite RPG (Rocket Propelled Grenade) launches a powerful proximity grenade that can bounce off walls. The grenades explode after a short period of time, or when they come into contact with an enemy. They have a fairly good area of effect and are quite powerful.
The weapon is great for firing around corners, and killing enemies which aren't in plain sight before Jak rushes in. It can also be used for taking on smaller enemies in medium range before approaching them in melee combat; while it uses more ammunition to perform an attack, it kills multiple enemies in one go, which can be faster than using the Blaster.
The Plasmite RPG can be good for taking on hordes of KG Death Bots or smaller Metal Heads, but also for defeating the stronger enemies quicker than with other weapons Jak has at the point when it's acquired (or, for those using it later, when Dark Mod weapons have ran out of ammunition). However, note that the grenades should be used sparingly, as it chews up 10 units of ammo per shot. However, as with most weapons in Jak 3, it can be given an "efficiency" upgrade from the cheats menu, thus, it only uses up eight ammo per shot.