Shard bombs are relatively weak bombs that excel in spreading damage. By themselves a shard bomber will only be able to soften up enemies for allies without creating the knockback of the popular blast bombs or the lack of damage haze bombs have.
The shard bomb is basically the noob friendly bomb, it has a good charge rate, not too much knockback, decent damage, high mobility, and most important the fact that it hardly ever misses.
A group of shard bombers that stick together and place bombs near each others will quickly decimate a group of monsters.
The shard bombs have a type distribution that allows it's wielders to pick any type of damage they want.
The best shard bomb (in my opinion) is the Shocking salt bomb.
It provides great slime damage, good gremlin damage, the shock status does good damage to constructs, and the beasts (with a simple mindset) will also take fair damage. This allows it to cover 4/6 monster types.
But the number one reason to use shard bombs is if someone else is using one.
I'm no bomber, but I disagree with a lot of this.
[...] a shard bomber will only be able to soften up enemies for allies without creating the knockback of the popular blast bombs [...]
The knockback of a shard bomb is rather unpredictable as there are several points of explosion, which would not be a big problem if it was not because multihitting an enemy makes seem rather random. A blast bomb has predictable knockback and a rhythm in its explosions as long as the bomber does not screw up (or they time their bombs to interrupt/hit more, in which case it's a good bomber and it shouldn't be a bigger hassle).
The shard bomb is basically the noob friendly bomb, it has a good charge rate, not too much knockback, decent damage, high mobility, and most important the fact that it hardly ever misses.
Shard bombs evidently have crappy damage, along with way too many bugs that just screw you over. Additionally, I'm rather sure they have a steeper learning curve due to the extremely long time between dropping the bomb and having the shards explode. And the bugs. You need to understand and avoid the bugs.