I don't know the true effect but my experience have been some of both. I've fished the banks hard with no bites then a semi hard shower starts and ole nelly, can't keep up with the bites right along side bank in a foot of water. But also you have to account for the time of year as well. When I experienced this explosion it was in the middle of the summer when showers were rare. also I've found that a lot of fresh water can slow them as well. This is just my observation. I'm no expert by any means, lol.