The answers to the questions are yes, yes, yes & yes.
They provide a food source for bait fish when the algae builds up. Some areas are so tight that they also provide cover for bait fish. Crappie use them for protection from other predators and use them to ambush bait fish. Sometimes the Crappie will be outside the condos and beds feeding if their food in the area. The most important thing to think about a condo is it provides a place for bait and crappie to congregate narrowing the amount of water you need to cover. I fish what ever I put in and what I can find.
G.