The Dark Briar Barrage (DBB) is a piercing, blast bomb style weapon. It has a high knockdown/flinch chance and minimal knockback. Many soft bodied enemies (small fiends, small beasts, nearly every gremlin species) are subject to that flinch. At a high enough CTR this bomb can flinch lock enemies into place, any enemy within the blast range of the bomber is to be considered incapacitated, this makes the job of other knights much easier because they have to deal with less monsters.
The DBB becomes less effective as a team support weapon when: monsters are knocked out of the bomb range, when the more dangerous monsters are not targeted by the team (constructs, and jellies should be kept away from the bomber when he/she is flinchlock/chainbombing), when the bomber targets the wrong monsters or is too aggressive (targeting monsters that are being attacked by another party member).
As a sword user try to target monsters that are not in the blast radius as those are now helpless and you should focus on bigger threats.
Gunners should play according to the knockback of their gun. Weapons like the blitz needle can get easy charges on the monsters, while antiguas can spam regular shots beside the bomber to draw the agro of far away monsters thus pulling them into bomb range.
Guns with knockback should try to lead monsters into bomb range and then once the monster is in range go try to pull another into it.
Other bombers should use weapons that compliment the DBB, such as: more DBB, haze bombs that inflict DOT or poison (freeze and stun are ok but the others are better), Dark retribution.
Shard and vortex bombs are iffy while blast bombs should not be used close to the DBB (so as not to knock away the flinch lock targets)
If a team fails to support a DBB user they may resort to bombs that promote self preservation (nitronome) rather than team support.
@Holy-Nightmare I'm currently training to master using the DBB due to it being quite effective bomb because of it's knock back and it's offensive features.
For new time users of a DBB, I'd suggest using simple tactics to use the DBB effectively.
1) Use the DBB for it's AoE (Area Of Effect). Some bombers like using this as an offensive bomb for targeting monsters one at a time however I'd suggest trying to take down enemies at the same time. This way, it won't be such a hassle. In team fights/groups of monsters, it can help cover a small area in one go and help defeat enemies in an instance.
2) Be wary of enemies. Although you may blind your enemies at the sight of the jumping Snarbolax, it provides 'minimal knock back' as Holy-Nightmare said, so I'd suggest trying to move to dodge range attacks as well as simple Melee attacks whilst bombing with a DBB.
3) Lure your victim in. If in a situation where you are trying to kill an enemy as soon as possible, lure them closer to the middle as they are subjected to all of the explosions if you stayed in the same area.