Confused about Booming Blade

[Azreal]

I'm not sure why it's so popular for builds. Can someone explain how they can reliably get that second damage to go off to make it good?

[Limited Gish]

I'm not sure why it's so popular for builds. Can someone explain how they can reliably get that second damage to go off to make it good?

I really like it on Swashbucklers. The ability to run in, hit 'em, and run out helps build damage up on big slow guys with low range. Mobility feat gishes can do the same thing. V.Human mobility Storm Sorcadins pack quite a punch.

[HolyDraconus]

I'm not sure why it's so popular for builds. Can someone explain how they can reliably get that second damage to go off to make it good?

What makes the SCAG cantrips (well, two of them anyway) so good isn't just that though. Its the fact that its essentially an extra attack up front. A Rogue with Booming at level 8 is doing the equivalent is most cases of 3 attacks off that single one. Since the rogue has one attack anyway, making it huge is just a plus.

[Drayelock]

It is not so much the damage but the option of "soft control" and is really effective if you have a mobile character that has ways to get out of opportunity attacks or has a high enough AC you are willing to risk them hitting you to get out. If they move after you to attack you on their round after you leave, they take additional damage. If they stay because the creature does not want to take damage and move you've reduced their action to sitting and doing nothing or resorting to ranged damage.

[HolyDraconus]

listen to the dragons... they got the right ideas

[imanidiot]

I'm not sure why it's so popular for builds. Can someone explain how they can reliably get that second damage to go off to make it good?

Look at it side by side with the other cantrips that are available for those builds. It's not that Booming Blade or Green Flame Blade are that great. It's that the other cantrips for the most part are worthless most of the time or just a basic attack for a ranged caster.

[Drayelock]

listen to the dragons... they got the right ideas

Dragon Bros unite!

[Willie the Duck]

I'm not sure why it's so popular for builds. Can someone explain how they can reliably get that second damage to go off to make it good?

There are specific builds for which putting your enemy* in a situation where they either take the damage, or spend the round not getting to attack. A rogue who can attack and then withdraw. A polearm fighter with PAM and warcaster (hit someone with booming blade as an OA when they are 10' away, see if they advance). Or the ubiquitous sounds-awesome-but-good-luck-getting-the-rolled-stats-to-pull-it-off shillelagh-SCAG-PAM-Sentinel-Spirits-Guardian-Thorn-Whip blender (highlights: they come up to you with a BB attack and Spirits Guardian up, you can either run away, taking the extra BB damage, or stick around and eat area-effect damage and get the same thing next round).
*presumably not one with a great ranged attack, so what they want to be doing is closing for melee

But beyond that, SCAG cantrips just let characters who otherwise probably should barely bother melee attacking (and only if they don't have anything better to do) do something with their melee attacks. GFB probably is more likely to trigger its secondary damage, but more things are immune to fire, and part of the damage is based off your spellcasting stat (so if you are, for instance, an Int 8 Arcane Trickster picking up either BB or GFB as their Int-based cantrip, BB looks pretty good just from base damage alone).

[DarkKnightJin]

It also makes it so gishes that don't get multiple attacks have some scaling damage, because cantrips.

The Rogue with BB/GFB could do a single attack with a Rapier for 1d8+Sneak Attack. After 5th level, they could also be doing Booming Blade, getting 1d8 from Rapier, (1-3)d8 from BB, and their Sneak Attack dice if SA would be triggered. Because they're making a melee attack as part of casting the spell. Then they can Cunning Action Disengage and GTFO to try and lure the enemy after them. Or leave them with the party Fighter or Barb.

Pretty much a case of 'Damned if they do, damned if they don't' in this example.