here's my 2 cents;

1. I personally feel crappie relate to structure tighter in muddy water than in clear water. I think the effects have to do with sight, and the effects that muddy water has on temperature. If it is sunny, the water will warm quicker in muddy water.
2. I think you can get a lot closer to the crappie in muddy water, because it does effect visual field. I think it's probably a lot easier to doodle with just 3-5' of line on a 10' jig pole than in clear. In clear you have to stay off them & use corks so not to spook them. That's what I think anyway.