Perhaps you could check the command reference to find out for yourself?
Most of these questions are covered in the "help".
EntityFX 4 - I've never used it,
EntityFX 8 - if you want something to ignore fog effects and be visible
EntityFX 16 - if you want backfacing triangles not to be culled, ie visible regardless which side they are viewed from.
EntityFX 32 - used with vertexalpha to ensure alpha is displayed at a per vertex level.
Most of these questions are covered in the "help".
EntityFX 4 - I've never used it,
EntityFX 8 - if you want something to ignore fog effects and be visible
EntityFX 16 - if you want backfacing triangles not to be culled, ie visible regardless which side they are viewed from.
EntityFX 32 - used with vertexalpha to ensure alpha is displayed at a per vertex level.