Smaller coils are good for getting closer to equipment in tot lots. In trashy areas they can detect coins without a piece of trash under the coil too. Several years ago a friend of mine and I got a call to search fro a ring. Instead of a ring, we ended up looking for a white gold diamond post earring without the back. Using it's mate, we discovered that it wouldn't even read on our 8" coils. By almost rubbing it across a four inch coil, we got a reading. On our hands and knees, we scrubbed the area. After several hours, first we found the back (also white gold) and about half an hour later, the earring. I don't know what it was worth but they gave us each twenty dollars for our efforts. Without the four inch coil, we would never have found it. This was on an old Whites 6000D.