If you look at the photo below, you will see evidence of why a home in an area that gets significant rainfall should have gutters and downspouts. The wood fascia, below the roof, has had heavy runoff water routed over it for about five years. Wood that is subjected to heavy moisture will eventually decay. Fungus is moving in on us here, slowly but surely.
If a roof have proper overhang, over the gutters, that wood will be afforded a great degree of protection. And that is very helpful in the long run. This home, like many houses that do not have gutters, is located in a heavy snow region so the owner is probably reluctant to install gutters. They can be prone to coming down when snow and ice collect inside of them. But, without the gutters, the wood is under constant assault in this wet northwest climate.