Shard is an addon made to facilitate Drain Soul farming.
It takes a user-defined maximum number of shards (default 28), and will delete any excess shards. It was made to allow liberal use of the 15% mana return while farming/questing without having to manually delete tons of extra Soul Shards.
To change the maximum number of shards allowed:
/shard [number]
Calling this command will automatically delete any excess shards, so /shard 0 will delete all your Soul Shards.
You can see the current maximum shard number in the frame below your minimap (it is movable), or by typing /shard max.
Variables are saved per character.