In CA, you can buy a second rod stamp (goes on your fishing license), it is about $8. You can only have a second rod on lakes and reservoirs, no river fishing with a second rod.
Not only does it bring in a bunch of money for the state, it is nice to be able to experiment with one lure, and still have the old confidence lure in the water. A second rod also allows me to fish at different depths with the downrigger.
I usually have two of us in the boat, with 4 rods out. It is very fun when two rods light up..."you get the net," "no, YOU get the net, mine is bigger." "Its my boat, you get the net!"
You get the picture. It is very hard to net someone elses fish while playing your own.
On one occasion, we had 3 rods go down. My buddy grabbed his rod, and I grabbed both of my rods. That was a mistake. I had never thought of it before, but I found out that if you hold two rods, you cannot reel in either one. I had to stand there and try to feel which fish was bigger. It was not easy because my buddy kept yelling "GET THE NET!"