Rod, and the line, and the gear ratio of the reel. It's all kind of optional, but it improves the outcomes for sure. Three examples that come to mind:
1) a shorter rod with some give for jerkbaits. The way you fish it the tip really needs to be down, and it is much easier to do that with a shorter rod. And the give helps with the smallish trebles on most. Lighter line than most of my setups. Don't care much about reel speed.
2) The rod I use for big single hook swimbaits is long and has enough stiffness and backbone to get the owner beast to penetrate properly. It'd be a train wreck with treble hooks. Heavier line than most setups, prefer a 7.x or better to be able to catch up to them when I'm getting bit from behind.
3) for me, I'm much more accurate flipping with a shorter rod. I can't explain it but it's like night and day. But I wouldn't want to use that rod for casting a jig. Standard line, fast reel so I don't have to reel as much getting it back to the boat.
And... 3-5 rods is plenty to get the job done just fine.