foundation issues. The gutters take the rain water away from the house at the downspouts. If the water just rolls off the eave it will soak into the ground on the edges of the house, will absorb into the foundation block and in time the house will sink, the foundation will crack.....$$$$$$$$. That also why it is imperative to keep the gutters clean if the downspouts clog it back fills the gutters, the weight of the water over time will pull the gutter away from the house, it will also start absorbing under the shingles and cause rot at the eaves.

My Mom put leaf guard on her house several years ago and did very well for her and I since I was the gutter cleaner for her. Has since sold her house but the did a nice job for her. I don't have them, my gutters stay pretty clean, no time cleaning them over the year.