Trained to throw explosives accurately at extended distances, Grenadiers were implemented to allow GDI to counter enemy infantry, fixed defensive emplacements, and buildings.
Grenadiers are multi-purpose infantry unit most effective against clusters of enemy infantry units and even armored vehicles (though due to their squishiness, are best kept at a distance). Grenadiers are very effective against enemy buildings or when placed behind natural and artificial barriers, like cliffs and walls, allowing them to pelt enemy targets with relative impunity.
When a Grenadier is killed, the grenades they carry tend to explode. As a result, they operate best when spaced out, away from one another and other infantry.