Wow I'm glad I asked this question so many good ideas here.
What I did today on the water was use a 4' shot line (also brought 6' for deeper water). To answer your question Cork, while there are many benefits to shotline listed above, I personally use a shot line to save time on the water. I'd rather spend a few hours at home rigging up my gear than spend 5 minutes here and there on the water rigging up a whole new set of shots on my mainline every time I need to re-rig. For instance, my smallest float (requiring the least shot to cock properly) is 4g. I know I'm never going to rig less than 4g on to my setup. So I may as well have 4g shot lines pre-made. If I need 4g, I tie on the shotline and leave as is. If I need 7g, I add 3g to my 4g shot line and this saves the time and hassle of awkwardly adding 7g of shot in various denominations in cold or windy conditions on the water.
I use a a shot line some are pre made
Two swivels on either end usually @ 4 ft. Everything goes on the shot line, shot and float.
I usually use trilene xt 6 lb. Xt is extremely tough and I am not afraid of sliding the shot up or down the line. Haven not lost a float in a while.
Swivel.......float.....shots......swivel then my flouro line to hook.
Shot line are usually used with high VI's lines.
Also you can slide to adjust you depth of your presentation
jc53, what do you tend to do when you have to fish deep water? If your float is on your shot line below the swivel to mainline, what would you do when you have to fish water requiring more depth than your shotline? I've run into this problem, and typically I will remove the float from the silicone tube, slide the tube up and over the swivel so it's now on the mainline, and reattach the float. Seems to me there's really no easy way to incorporate shot lines. And without them, there's really no quick way to re-rig or switch rigs.
Today I used the following setup:
Mainline (store spooled it up, think it's 10lb test)
Shotline which is 4g of shot in AAA and BB on 4-6' of 8lb test fluoro leader (could go mono too)
Leader which is 2-3' of 6lb test fluoro flyfishing tippet with no weight on
This way if the hook snags I only lose the leader which is the least painful to have to rig up on the water. If the shotline itself were to get snagged, I'd lose everything below the mainline swivel, but I know at which point on my system the line will snap. Lots of times I'll keep my float this way.
Thanks for the replies guys, keep them coming.