Coral,
Shop gave you a good general answer, so let me give you an example of one way I use bid groups (I use them all the time!).
About every 6 months, my HP printer needs a new ink cartridge. If I go to the local office supply store, I can buy one at retail for $25 - $30. However, I can pick one up on Ebay for about HALF that amount INCLUDING S&H. There are probably about 100 of my type ink cartridge up for auction on Ebay at any time. The KEY is I only want to win ONE!
Now I COULD snipe an auction, wait to see if I win, if not, find & snipe another, etc. until I finally win one. (Ugh! What a tedious PAIN!) OR I could snipe several auctions selling the same ink cartridge, but then I'd need to babysit(check) my snipes religiously to see when/if I won, so I could then CANCEL all the other remaining snipes, else I could very probably end up having MULTIPLE wins when I really only wanted ONE.
That also is a lot more work and more restricting than I REALLY want to put up with!
OR....I can set up a BID GROUP! (In fact, I even have an empty ink cartridge bid group set up right now ready to go for the next time I need one!)
1) I set up a bid group (I named it "InkCart.") like Shop described.
2) I browse the ink cartridge auctions and set up my snipes like normal, EXCEPT instead of submitting it to "My Snipes", I submit it to my "InkCart." bid group. (The last time I did this, I had over a dozen snipes scheduled to bid on ink cartridges over about 3-4 days.)
Now here comes the really neat part! AS will snipe ALL those auctions in that bid group UNTIL I win ONE (I actually LOSE most of the auctions due to "Bid too low" or "Proxy outbid" because I'm doing lowball bidding looking for a bargain!!). Finally, when I win one of those sniped ink cartridge auctions, AS IMMEDIATELY and automagically CANCELS any remain snipes in that bid group -- I don't have to do anything! That protects me from winning MORE than I want! I can also keep adding snipes to that group UNTIL I win however many I indicate when I set up the group. I've only ever wanted ONE of what I've set groups up for, but AS allows you to setup for however many you want to win.
Once you become familiar with bid groups, you'll think they're the greatest thing since sliced bread and use them all the time!
One key thing to keep in mind: Once a bid group has successfully won the number of items you wanted, it becomes locked/inactive. If you decide you want to win MORE of that particular item, you'll need to set up a new bid group (no biggie!).
Hope this helps!
Snipe on (in bid groups!)
Jabbergah