The point I was trying to make to a beginning fly fisherman, about the leader being close to the length of the rod, was for easier casting and control and to keep it simple in the beginning. What Maurice said is exactly right, the 1.5 – 2x the water depth is the indicator depth. I generally use a leader formula similar to what Maurice uses. I start with a 71/2 tapered leader tapered to 3x or 4x, and add 11/2 – 3’ of 4x or 5x to it, depending on the depth of the water (tippet length), and the water clarity and fly size (tippet diameter).
If the water was 4 or 5 feet deep and swift, I probably wouldn’t use an indicator. With all the weight it would take to get to the bottom, I don’t believe my nephew’s plastic Snoopy bobber could keep it afloat. I often see guys with their indicator all the way up their leader next to their fly line, wondering why they ain’t hittin’. I wouldn’t expect to be able to see the indicator move when the fly is 9 or 10 feet from the indicator with all the slack created by the heavy leader bowing in the current. I fished the Ausable River in the Adirondacks this past season, and that river gives new meaning to high gradient fast water. There I resorted to using no leader on certain sections of the river. I tied straight 3x to my fly line and used heavily weighted flies and shot to cut through the current to reach the bottom. That’s an extreme case.
I find an indicator is necessary to fish across multiple current speeds on the stream. Using it allows me to hold the line off the water and mend to the indicator. If I use an indicator, I adjust it to 1.5x (slower current) to 2x (faster current) the depth of the water. If I don’t touch the bottom on the drift I continue to add weight until I do. Fine adjustments can be made by moving the indicator after you have the right amount of weight. As I move, I constantly adjust both the indicator depth and the weight until it’s right again (ticking the bottom). Where I can wade out and fish in the same current lane I use a similar leader/tippet rig without an indicator. I fish either similar to Czech nymphing (off the tip), or Joe Humphries style (straight upstream). When I fish that way I use feel as much as sight to detect strikes and feel the bottom – like the old bait fishing days. You can cheat a little and use the a little strike putty, small pieces of fly line on your leader, or brightly colored line for better visibility.
I use the same leader for drys and build it out in steps to 4x, 5x, or 6x, depending on the water clarity and the size of the fly. My dry fly leader usually ends up averaging around 12’. I only tie on a longer leader in special situations (spooky trout clear water). Another special situation is when I use a 6-7’ rod for small stream fishing. I scale down the leader/tippet to around 7’ total for better control in tight casting areas. I custom tie a steep tapered leader for those conditions.
I usually use the butt end of knotless tapered leaders and rebuild the end taper to suit my needs. You can also tie a knotted leader from scratch using the leader formulas available. A few leaders last me a long time. Like Maurice, I too have been known to “forage” for leaders on the stream or in the parking lot, some I throw in the trash (where they belong), some I rebuild. You don’t have to use the leader exactly as it is right out of the package. I experiment with ways of tapering your own leaders to meet conditions. One rule that applies is don’t taper a leader with diameters greater than 2/1000’s (2 tippet sizes) at a time near the tippet end of the leader. In other words you can’t go from 3x to 6x in one step. Good Luck.