I am a belter  but just wondering ,I know the difference looking at them but what are their different uses on the job

it is personal prefrence man... some use pigs some use sponges. I only use a pig if i am uncertian if my pipes are clean

There's the obvious cost difference. Its alot easier to blow a sponge into a mixer and forget about it, sometimes that piggy's hard to find! Pigs or godevils do a better job and last for a long time but they're also a little more dangerous since their solid heavy rubber and shaped like bullets!