Bleached Shells are mostly used by Warriors wanting the Crimson Carapace Shield (one of my favourites) which is available from a desert collector upon trading in 5 of these shells. At one point their popularity had peaked with shells fetching over 2k each.
I personally found bleached shell farming a bit of fun and enjoyed mucking about with my invinci-monk getting shells and shields for my characters and my friends & guildies.
Basically you start at Dunes of Despair and proceed through the teleport having disposed of the four forgotten warriors/rangers by that teleport.
Once you have moved through the teleport head to the right where you will notice some large stone pillars. Sand Wurms (usually 3-5 per run) will pop out of the ground around here. Using the build in the builds and templates section you can proceed to send them to their doom!
Btw, I'm in there somewhere:
