Sleepy,
Welcome to BRS!
The major advantage of participating in a group buy, like this one is saving on shipping. The savings may be in the form of free shipping when a $ quota is met, to others where shipping is split among the group. Other perks may include additional discounts when the order is large enough, to free frags, which may or may not be distributed to those participating in the group buy. But this varies from vendor to vendor, and usually not stated ahead of time. Pickup is at the person work place or home that initiated the group buy.
Other group buys involving non-corals are posted from time to time from sponsors (ie bulbs), which give discounts when certain quantities are ordered, or quantity discounts (increasing discount as more are ordered). Pickup is usually at the store, or maybe at the meetings
Hope this helps. Have you joined BRS? Its a great way to buy/trade corals and meet new people.
Ron