For an overview of rocket launcher types in various games, see Rocket Launcher.
The rocket launcher is the heavy weapon of choice for assault teams facing clusters of opposition, preferred weapon of the Master's more destructive super mutants.
“A Rockwell BigBazooka rocket launcher. With the deluxe 3 lb. trigger. Fires AP or Explosive Rockets.”
In Fallout, this weapon was very useful, capable of doing massive damage to clustered targets from a long-range. In Fallout 2 however, by the time the player finds the weapon and can access a consistent supply of ammo for it, they're likely near the end of the game, where enemies tend to wear power armor of some sort. Even then, the effective-yet-oddly-designed armor piercing rockets it uses can slice through most Enclave contingents with one or two blasts. Most enemies, including deathclaws and aliens, though, have very little explosion resistance, making packs excellent targets. Using this on a locked door will destroy the door but you can still walk through it.