Heavier

Current favourite lineup: Kiesel-Duncan-EVH.

I have friends asking what's the point of using a drive/boost pedal in conjunction with an already angry amp? Saturation. That's right, sometimes even the angriest amp in the world can't give you that pick sensitivity to play fast or manifest a smooth legato line. 

Next query, will adding a drive/distortion/boost pedal will definitely make your tone heavier? Simple answer- no. It will increase saturation (as mentioned above) but not heaviness. Say you have a Fender Twin amp, will hooking up a distortion pedal make it heavier? That's right, it's a no. Picture this instead- you, hooking up a Tube Screamer pedal into a MESA Dual Rect. You will get a heavy tone, definitely, but not because there's a Tube Screamer in there but because the Dual Rect has laden heavy tones to begin with. In conclusion, for heavy tones to happen, you must start with an amp with heavy tones to begin with. No amount of throat supplements would turn Elvis into Ronnie James Dio 😁