Well… good question.
I anchor as a rule until the water flows reduce greatly later on in the summer. Even then, once I’ve found fish, I’m on the hook to really maximize my presentation.
The fish “usually” aren’t scattered all over the dam. Current levels will dicate the preferred holding areas for fish on a dam and that usually puts the fish on the tip…. or on the inside…. but very rarely just scattered completely along the length of the dam. So I make an initial descision on what position gives us the greatest chance for sucess…. based on experience I’ve had fishing that particular dam as well as how things look to me. And I throw out the hook and we fish that area completely.
I can’t tell you how often we find a little sweet spot that only becomes apparent after making repeated and only slightly adjusted casts to a dam from an anchored position. That kind of accuracy isn’t possible when your on the electric. You won’t even realize how much you’re sliding around and moving in and out from the dam until you try to do so next to an anchored boat.
Besides, the cranks I cast are pretty heavy and will go a country mile allowing me to cover a huge chunk of a dam from an anchored position anyway. Very few dams are long enough, and have enough ground worth fishing, to require me to re-anchor to get at water I couldn’t touch from my previous spot.
I’ll take precision over quantity and convenience ANY time. Hope this helps.