Let me restate. What are the the 3 most recommended accessories in the commuting forum? I'd say that they are lights, racks, and fenders. So in my mind asking how effective fenders are in the commuting forum is much like asking how necessary lights are. I don't think the results are going to surprise anyone. I'm not saying it's not a worthwhile question, only that the answers are pretty predictable.

There are many who consider fenders a "must have" and because I like be contrary, I like to point at that not everybody needs them. And, again, because I like to be contrary, I'll say that I have fenders on my bike neither to keep rain nor water off of it. I find them pretty ineffective at that. I have them to minimize the amount of wet grit and salt that ends up in the drivetrain. During certain times of the year I have also like to minimize the amount of water hitting my feet. I think that they're pretty effective at keeping spray off your back, but I change clothes when I get to work, so that's not a huge concern of mine.