Barrel Swivels for fishing, what are they used for?

[genwuine_looney_friend]

What are the Barrel Swivels used for? I bought some with the Interlock Snaps so I could easily switch out the crank baits however I noticed when I used them. It made the crankbait go lower to the floor of the lake. I"m think it is b/c of the weight of the barrel so what is the purpose of these if not for the easy switch of lures. Is there something else that won't increase the weight.

Thanks!