"FX Alembic Selection" is a solution to speeding up the loading of the Alembic SOP. As the above images, we only need few primitive(s) from the Alembic cache, usually Hi-Res cache. The simple way is to blast out the rest primitive(s) by selecting. But this isn't avoiding from loading full ABC cache.
By picking from the "Object Path" in alembic SOP could avoiding from loading full cache. Here comes the "FX Alembic Selection".
The "FX Alembic Selection" will read the displaying primitive(s) from the blast SOP on the right and write the specified object path back to the alembic SOP.
Now you get the clean alembic SOP reading the primitive(s) you need only.