When do you use barrel swivels? I would like every scenario you would use one.

Carolina Rig

Drop shot.

Okay I thought they were used more often for braid. 

Used for double fluke rigs. As for line I've seen used on all types of line. 

Carolina rig, dropshot rig.  If I ever did a high/low setup using bait in the ocean with a braid mainline, I'd use one there too.  Basically anytime I'm using a setup where I'm attaching my braid mainline to a fluoro or mono leader I'll use a Spro Power Swivel instead of a line-to-line knot.

C-rig, rigging my droppers for catfish setlines 

Carolina rig, or any time there is a split-shot on my line.

When i do use a swivel, its always a Spro Power swivel.

This is not gospel, but it may help:

USE SWIVELS ON

Carolina rigs

Fluke rigs

In line spinners (If line

twist occurs)

 

USE SNAP SWIVELS OR

SWIVELS ON

Standard Spoons

Mepps Syclops

 

TIE DIRECT TO

Buzz  baits

Chuggers (or split ring/duolock)

Jigs

Frogs/rats

Prop baits

Spinner baits

Stick baits (i.e.Zara Spook)

Tail spinners

Weedless spoons

Weight forward spinners

 

TIE TO SPLIT RING OR

DUOLOCK  SNAP

Crank baits

Lipless crank baits

Jerk baits

Blade baits

Jigging spoons*

 

* Swivel if desired