It is not necessary at all but it makes it easier when fishing with kids or people that are not experienced. All I have to say is let out X feet of line and you know they are in the strike zone. I also like the ability to set up off of a piece of structure and then creep up on it with the lines set to the correct depth.
This x2.
I have 4 trolling/bouncing rods set up with Okuma coldwater low pros. They work so nice for running bottom bouncers. I can hand one to my oldest daughter or to my wife, or a family member or friend and say “let out 35′. It just makes sense to use those setups. Load them with 10 pound XT and you have a dual purpose trolling and bouncing setup that covers a lot of scenarios. I can pull spinners all day in 25′ of water, then unclip the bouncer, throw on a husky jerk, let out 100′, and troll the shallow sand after sundown. Less rods in the boat.