We've only got the builder supplied guttering on our house - the small section that is above the front door. After several years, we've noticed that the water running straight off the other areas of the roof (where there are no gutters) tends to beat a small rut in the grass where the water hits - it parallels the roof edge. Not the end of the world but it is noticeable.
Gutters help divert the roof water runoff away from the house foundation which is always a good thing.
Bill
