It is one way to change the tune on the dyno but for a street car I'd put the level in the middle of the glass and leave it alone.

An even quicker way to change the tune on the dyno is to use the idle feeds. The idle feeds will give you a full point of AFR. We got in the habit of just turning the idle feed screws if the engine was within a point of where it needed to be. Much quicker than opening up the carb and changing the jets.

Once again, I don't think I'd tune a street carb with the idle jets but it can be a fast way to try something.