I have a house in the Seattle area. A realtor told me to trim all the bushes so that they don't touch the house and wood fences before putting it for sale. Is that really necessary? What's the harm?
It shows a lack of care for the home. Bushes against the home or a wood fence are an entrance point for pests (termites, ants, etc). It also adds more wear and tear from abrasion that you wouldn't have from just the sun and rain. And for a buyer, a bush growing against the home could be hiding a problem.
So if you want to make it look as if you've been caring for the home, I'd trim it back before the buyers see it. And for your next home, I'd recommend trimming them back as well, so you are actually taking care of your home and not just making it appear that way before the sale.
Another thing the brush and bushes do is create a more humid and shaded environment. This will promote mold growth which can cause its own issues (rotting, allergies, etc). If there is mold growth (black splotchiness) or algae, there are several cleaning products that you can pick up from a local hardware store. They come in bottles shaped similarly to regular indoor spray cleaners but have a hose attachment instead. Some products work better than others, and some are "greener" (plant-safe, environmentally friendly). We just used some on a rental property a few months ago and the siding (on the north end of the house) looks new. I wish I could remember the brand that worked best, but I honestly can't remember. Maybe an employee could help provide recommendations.
In the Great Pacific Northwest, land of moisture and people that rust instead of tan, anything growing against the side of a house contributes to damp and mold growth.
It can also serve as a bridge for ants to evacuate the ground during the first rains, so they start crawling the siding to find voids where they can overwinter.
The absolute worst is Ivy. I personally value any house that's had any quantity of Ivy growing on it at demolition costs. The suckers it uses to cling to the siding break through paint. The moisture buildup leads to areas that never dry out, allowing black mold to grow in the breaches in the paint. It will push its way through the T&G edges of T-111 siding, despite it being well nailed down and proceed to attempt growing inside the wall. The worst instance of this had an ant nest filling the wall.
Another thing to consider in the PNW is wildland interface properties. Laws are going into effect that penalize property owners for maintaining hazardous situations where fire can spread off the property and into adjoining land. One of the major no-nos is having stuff growing against housing and under decks.
Plus it just plain looks messy.