Depends entirely on where you fish. But I can't imagine limiting myself to just 3 lines. And extra spools? Not a chance. Fully rigged rods. To me, for stillwaters, I think three outfits is the minimum.
1. Floater
2. Intermediate (prefer a full intermediate but ok with a sink tip).
3. Fast sinking line
Years ago I went with the extra spool route. And it is much less expensive. But its also much less effective. The problem isn't the time it takes to change from one line to the other. The problem is that far too often its likely to need to change multiple times throughout the day. Switching lines back and forth becomes and exercise in a lot of wasted fishing time.
Then there is this scenario. I am fishing just off the bank out toward a drop off. Using a floating line and indicator using a midge off the bottom. Then I see a big blow up along the shoreline. I can grab my intermediate setup and get a cast in to the area in say around 30 seconds. The fish may or may not still be there. But if I have to reel in, change lines, tie on a fly on the other line there is just no way that fish is going to still be there.
