crayfish have a way of eating the vegetation if left unchecked. No vegetation equals crayfish digging in the bottom and this gives muddy water. That can be a pro or a con depending if control of vegetation is your main priority. (muddy water equals poor light penetration which means that vegetation can't get a start)
On the other hand, clearer water produces weeds, but also helps the food chain and keeps the tiniest members of the food chain going.
On the other hand if you have rip rap or other natural crevices for them to hide in they can maintain a population even with lots of hungry predators looking for them.
